About hobbles - have I used them on kickers and pawers in a trailer - yes...would I recommend it -NO. Your horse needs to be able to balance himself, and if you have an emergency where you need to get him out of the trailer NOW, you will have to get under him and get those hobbles off before you can unload him. Is he trailered alone? I had one horse who could get the trailer rocking and rolling when he was trailered solo, but was a complete angel when trailered with a buddy...and he was a champ at loading and unloading too. Sometimes it can be as simple as loading on the other side or travel with him riding backwards or traveling loose...just making things different enough to break the habit. If that doesn't work, when he starts pawing, tap the brakes hard enough so that he has to put his feet down on the floor - not enough to cause him to fall, but enough to get his attention. If you don't want to do that (it can be hard on your transmission and hard to do if you find yourself stuck in traffic) you might try a shock collar...I had a friend whose horse would scream, paw, kick, you name it, in the trailer...she only had to hit that button twice in one trip - lesson learned...he now travels like a gentleman anywhere and everywhere.
If he only paws while the trailer is parked, shout "quit" and hit the trailer with a toy wiffle bat when he starts pawing...if you aren't close enough to do that, toss a rock and hit the trailer...usually the noise alone is enough to deter them.