Don't stop running when you are on the same screen as the necro, unless you are within the melee range with him. Sorc, Barb can ignore it because they can teleport/leap out of the Prison anyway.

Of course, it is impossible for anything to attack without stopping, but you shouldn't stop when you're not within an attack range when you're fighting necros. Spiral around them, try to close in for an attack, but don't just stop all of a sudden when the necro is on your screen. If you are in your attack range, of course you should stop and attack him. If he casts bone prison, he will first suffer damage, and then he will be trapped with you.