My fella isn't exactly a hardcore paw-er, mainly three to five taps at a time once in a blue moon if he's tired of waiting for me to finish something. If he's tied up and I'm not right next to him, I ignore, and then praise when he stops. His main trigger for it is at dinnertime when I bring him in from the pasture to eat, and his stomach thinks it takes too long for me to re-do the gate-latch. I'll basically ignore that, too, and take as long as he's willing to paw to finish with the gate. My being done plus a verbal "Good boy" is his reward for stopping the behavior. If he paws while I'm halfway in front of him, in reach of the foot, I'll swat him on the chest and back him up, then try whatever I was doing again. I've seen saddlehorses with their forelegs ripped up because a draft half-stepped-on, half-pawed-on them, and I have no desire to go through the same recovery process myself.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown