If my horse is acting up on the ground and I'm having a bad day where I don't feel like correcting him I go straight to the cold hose.
For example, today he tried to nip me for the first time... repeatedly. He got a smack in the face, but it was a bit late and he didn't seem to get the message. Took him over to the hose, started washing him off and the second he tried it again I put the hose on full throttle and blasted him in the face. It's easy and effective if your horse hates water on their precious little face like mine does.
He won't be trying that one again ;)