Guys staring at my girlfriend?

I do not know how to take it. I should take it as a compliment and I know that and maybe I sound insecure, but I think some guys ignore me when I spot them staring at my girl and keep staring. Could I be paranoid or I am being considered weak, because I don't, but these signs begin to make me wander. I am not a bodybuilder, not small either, well built and quite a manly face I must say. I am mostly interested in the answers of intimidatingly and big looking men, like a bodybuilder or a professional wrestler ( did these things happen to them too? How do they deal with it? How do they intervene or act if the situation calls it to? ) I don't want to look insecure to others and maybe if I will start being insecure, which I think I am starting to become an insecure person, how to deal with it. Thank you.