"The ultimate aim of martial arts is not having to use them." -
Miyamoto Musashi
Strategy
Utilizing subtlety to target attention away from us, while creating a board state from which we really cannot be threatened is the name of the game. This philosophy cannot be heavy handed. Most players react badly to blatant manipulation, so be cautious. Attempting to force a play that a smart player would choose willingly without intervention is likely to lead to revolt and loss of control. Choosing a more subtle defense that accomplishes the same thing makes the defense even stronger than an otherwise objectively stronger defense.
Notable Inclusions and Card Choices
Pillow Fort
“Your spirit is the true shield.” ― Morihei Ueshiba, The Art of Peace
Ghostly Prison, Windborn Muse - Classic Pillow Fort. Taxes attacks pointed at you, hence encourages attacks to be pointed elsewhere.
Maze of Ith, Kor Haven, Thaumatic Compass
/Spires of Orazca, Forcefield - Maze effects make the necessary commitment for actually causing an effect with an attack to be much larger. Take the biggest threat out of combat for each of these that you have. When facing this, most opponents will try to find easier pickings. While not technnically a Maze, Forcefield turns every mana producer, including every land, into an almost-Maze.
Delaying Shield, Solitary Confinement, Phyrexian Unlife - Each of these reduces the effect of an attack. When opponents have a choice of decreased effects against you or full effects against others, attacks often go elsewhere. Delaying Shield is great for making big symmetrical effects like Acidic Soil trigger a full turn earlier on opponents than on you. It also ensures that you never take damage that is considered combat damage, so you never lose Monarch. Solitary Confinement is sustainable with Monarch, and precludes the normal loss of Monarch. Solitary Confinement is the Pillow Fort card that you would almost always prefer to be under, but it costs you 2 cards a turn. That is a heavy price, even for Hexproof and immunity to damage. Phyrexian Unlife prevents you from losing when you go below 1 life, an effect that can turn one of your symmetric attacks into an asymmetric win.
Solemnity - This can protect from Infect and Planeswalker wins, and generally hoses counter strategies. card:Solemnnity, Delaying Shield, and Phyrexian Unlife can combine in any two of the three to keep you from losing the game to damage.
Duelist's Heritage - This is an interesting card. It may be the most subtle Pillow Fort card in the deck. It just gives a reward to people who aim attacks in a way that you like. People like conditions that make their deck to work better even more than they like avoiding conditions that make their deck, strategy, or chance of winning worse. Strange, but very satisfying. The reward they get also directly forwards your plans of using the offense of opponents to take out your opponents. It can also be used to double your biggest attacker. Fantastic card.
Key to the City, Curse of Opulence - Somewhat similar to Duelist's Heritage, but weaker. Still, through negotiation, you can not only redirect attacks away from you, but you can enhance the attacks that are directed toward your opponents. Key to the City seems to also be a relatively easy sell, since discarding a card is seen as an extra effect against you that makes the attack that much more worthwhile. Curse of Opulence has the danger of inciting retribution, and the incentive has diminishing returns the further into the game you get, but the bonus of ramp early on can offset this danger some.
Gisela, Blade of Goldnight, Wound Reflection - Gisela decreases damage against you and your creatures by half, and doubles the damage potential of every source not directed at you or your stuff, not to mention the fact that she is a large flying body. Standing behind her feels safe. card:Wounnd Reflection also doubles the damage potential or every source pointed at your opponents. Opponents will often attack each other to gain the damage bonus or either (or both) of these cards.
Rattlesnakes
“Fill yourself with Ki, invite the attack.” ― Morihei Ueshiba
No Mercy - Straightforward Rattlesnake. Attack me and I kill your stuff.
Kazuul, Tyrant of the Cliffs - When combined with the Tax effects above, this can generate a large offense, or even just chump blockers. This usually doesn't happen, because the threat of creating an army will keep them from attacking. If you are attacked, it can actually stop an attack, given that the trigger is the attack, not successful damage, and the Ogre tokens can be used to block. Excellent defense.
Vampire Nighthawk, Master of Cruelties, Queen Marchesa, and her tokens - Deathtouch deters a lot of attacks. It also makes people hesitant to block when they are used to attack. If you are attacked or blocked, they can work as removal. It is surprising how well these work for deterring attacks. One deathtouch creature can often keep multiple creatures from attacking for quite a while. This is a much more subtle Rattlesnake than No Mercy, even if it can only take out one creature per blocker, but usually just as effective.
Fogs
"The supreme challenge of a warrior is to turn an enemy's fearful wrath into harmless laughter." - Morihei Ueshiba, O Sensei
Teferi's Protection - Best Fog effect. Can be a Fog effect, conditional counterspell, or a personal anti-boarwipe.
Deflecting Palm - Second best Fog effect, can be an instant anti-Tall or anti-Burn wincon.
Batwing Brume - Also an anti-Wide wincon.
Comeuppance - Can also be either a Wrath effect or a second version of Deflecting Palm for noncreature attacks.
Dawn Charm - Modal Fog, serving as a Fog, a conditional counterspell, or can save a creature.
Word of Seizing, Disrupt Decorum - Word of Seizing is an instant speed Threaten effect that can remove up to two attackers from combat, acting as a semi-Fog and semi-removal. Disrupt Decorum is sort of a proactive Fog, eliminating the enemy attack step as a threat to your safety.
Notable Exclusions
Hissing Miasma, Blood Reckoning, Marchesa's Decree, Norn's Annex - The loss of life can add up, but I find that inhibiting the development of board state or causing loss of resources is more of a disincentive than small life loss. Life is treated as a resource that can be spent, and people do choose to spend it. These become weaker Rattlesnake cards.
Story Circle, Circle of Protection: Green et al, Rune of Protection: Red et al - The Circles are considered un-fun in my meta, and are discouraged. If I ran them, I would run Story Circle for versatility or the Runes for their ability to cycle.
Riot Control et al - Riot Control is a Fog plus. It stops the current attack, but it also gains life to offset the next attack. It also does not need to wait for an attack to become useful. Sometimes all it takes is a little lifegain to make your symmetric damaging effects into game winners. This extra lifegain turned out to not be worth the card slot, and it was cut. The vanila Fogs were not useful enough to hold a spot. Every card must either over-perform in it's function or have multiple functions.
Boros Fury-Shield, Mirror Strike - Both of these only target one attack from one attacking creature. This is not as versatile as either Deflecting Palm or Eye for an Eye for redirecting a single attack, and not as effective as Batwing Brume or Dawn Charm for stopping all combat damage. Still, these cards could be a consideration, depending on meta, but their CMC is getting a little high for inclusion.
Selfless Squire - One of the best Fogs in the game. It is a nonmbo with Solemnity, so it came out.