We've "hosed" down our resident bully Morgan with a hand pumped sprayer set to squirt. Stream of water is great way to break a habit but the trick is not let the cat see it when he gets squirted. You don't want him to associate the bottle with getting wet. You want him to associate bad behavior with getting wet.

We use the sprayer, when he has another cat pinned down and the poor victim is growling back. Sneak up with the bottle and we let Morgan have it.

If I'm playing with my omega cat Gracie, aka scare-dy cat, I physically pick up Morgan, turn him around and shoo him away. Sometimes I have extra toys within my reach and entice him with the extra toy, then shoo him away.