Don't pull on it, it should tighten up. There are many things that influence slippage, from improper ph to improper field care. Have you ever checked www.taxidermy.net ? Go there and click on forum, from there find the orange button labeled search, click on it and type in "causes of slippage" or something similar, get a drink and a sandwich and sit back and read all about it. I have your situation happen before, and it tightened up. Hope it helps.