How to tell my husband is smoking pot?

I wanna know what to look for if my husband is smoking pot. He admitted to doing it before but it was supposedly only a hit or two at lunch from work. I am drug illiterate I do not know what it smells like, looks like, nothing. I see some signs that I think may mean he is doing it but before I post them I want to see what everyone else says first so I can compare. My questions are this.1) how can you tell if he smoked it 2) what does it smell like on clothes and 3) what does it smell like before it is burned. PLEASE HELP!!!