http://www.central-mosque.com/fiqh/detdisfeet.htm there is a nice article in the above link, read it properly and try to understand it then beat the **** out of them salafis after taraweeh tonight :/JK
If they are ignorant brothers who insist on arguing, just tell them, "Sorry, I don't have time to debate with ignoramuses." Either it will make them feel good about themselves (thinking that they "won"), or it will make them question their own conviction. Either way, you wont be wasting your time.