My almost 5 YO neutered male dog has developed a liking for humping over the past 2 weeks. Have never had this issue with him before (excepting 1 towel that he seems awfully fond of) but he is now trying to hump DH's (and last night mine) leg on a daily basis. I can't understand why he has suddenly developed this behaviour. Any suggestions as to why and/or how to stop it (or is this actually quite normal)?