What is the best method to make a wool farm?

[angel_feathers]

I'd like to maintain a flock of around 25 sheep on a permanent basis to use whenever this task pops up in the clue scrolls, but the sheep from spawners don't regrow their wool even when they eat grass. What's the best method to make a wool farm? thank you.

 

[Whitecornsnake]

I would say some type of automation so like after you shear the sheep they get pushed into lava and killed