A suggestion for a simple craft-able that make farming animals much easier, a lasso. This would be crafted out of string like so:
It would work similar to a fishing rod, where the loop would fly out a few blocks like the lure and attach to a mob (possible objects as well). The mob would then follow or be dragged behind you until you right-clicked again to set it free. This would allow you to lead mobs to fenced enclosure where your sheep, pig or what ever it may be will stay until you do something with it. It could also be used on aggressive mobs although they will most likely be chasing you anyway.
A problem that could occur is the fact that mobs can randomly disappear when not in the vicinity. Maybe make it so mobs enclosed in fences can't randomly disappear?
Anyway just an idea i had when trying to farm cows, chickens and sheep.