Probably something like those sprays they sell to keep deer out of gardens etc.. I would imagine it wouldn't last to long. You can always set a trip line on the paths they are coming in on and rig it to spray fox urine on them or maybe pepper spray. One of those bear can foggers of peper spray would set them straight. Actually, when they ran into a big old oak 'cause they couldn't see from the pepper spray is what would set them straight. Horizontally straight that is!!!