I just got something called Rap Last,as my lippy mare chews on ropes & unties herself all the time.I sprayed some on a tie rope today while I was working on my gelding. She stood real close, but I never saw her touch the rope today, which is a first. I've seen it on ebay
also, but be careful of shipping charges there. Best probably to buy it local, even if it has to be ordered specially for you. It seems to work.