My friend Henry had a dog named Rex, that LOVED to ride on his XR500. As soon as Henry started the bike, Rex would jump up the tank. (In fact, if anyone started a thumper, Rex would automatically jump on; nearly knocked me over on my FT500 once!) Henry fastened a piece of thick perforated rubber mat to the gas tank, so Rex could get a bit of grip. They didn't just putt around, either: hard-core trail-riding, berm shots, and wheelies were the norm.