Basically, a friend who is very insistent/opinionated commented on my use of the word 'of' in this sentence: Rom’s hand slid it’s grasp of the man’s arm. He's saying that it isn't 'of' but should be 'off'. Now, I agree that that is a valid word to use, but 'of' works as well. Am I wrong in this? I'm certain I've seen it written that way, and it doesn't make any lack of sense in either context to me.