My foal chews on EVERYTHING too! Actually, he's 1 1/2 years now, but he still chews on whatever he can get his mouth on. I was told by a trainer I am working with that's he's teething and will be doing that for a while.
He also ate other horse's tails until very recently. Thank goodness he seemed to quit that. I make sure he always has at least a little bit of hay between meals and that has helped. But I think the need to chew is a normal baby thing. I have had the best luck with coating tails, wood, lead ropes, etc, with habanero (sp?) pepper hot sauce. Basically the hottest cheap hot sauce I could find at the dollar store. Worked better than a bitter no-chew spray I bought.