Appearance (with Leather Boots)
A sitting Tamed/Neutral Wolf
Behavior (with Leather Boots) It can neither attack nor stand up (Actually, this behavior seems useless.)
And as suggested by some, lessen the barking
How to do: Right-click on an Aggressive or a Tamed Wolf. And as suggested by some, only Tamed Wolves that are yours could be given a Leather Boot
For an Aggressive Wolf, anyone can give a Boot anytime. For a Tamed Wolf, anyone can give a Boot when the Wolf is not targetting anyone or anything, including mobs. If it is tracking something or someone already, only the owner can give a Boot.
Effects: Aggressive: It and all other nearby Wolves will revert to Neutral and crowd towards the Wolf with the Leather Boots Tamed: It will not attack any mob or player and any previous targets will become untargetted Any previous targets become forgotten by the wolf. However, that does not mean they cannot attack anymore. (Note: The Boot lasts as long as its durability was when it was given. 1 durability point = 1 second/20 ticks)
Combat (with Leather Boots) None... Whenever a previously chewing wolf or the owner gets attacked, the wolf will stop chewing the boot and aid the owner in fighting. They will drop back the boot but applying the damage they have already done to it.
Advantages -A way to remove Wolf anger when you hit the owner -A way to neutralize angered wild Wolves -Lessened barking
Disadvantages -Immobility of the Wolf (unless pushed by a mob/player or using a Minecart) (I don't think giving the boot needs any negatives. It's not like adding a way to make the wolf stop attacking somebody requires a drawback.)