Stop A Unit Moving, yet still let it cast spells?

How would I prevent a unit from moving, whilst still allowing it to cast spells?

Set its move speed really low (like to 1), and you need to change the gameplay constants to that minimum unit speed to 1. Then its just a matter of slowing it down that much, say with a tweaked ability or a unit morph.

It can move, but you'd never really be able to tell.

Actually, I've solved it now. I used a modified ensnare spell, and it works perfectly. Thanks all the same though.