EDIT. smoking or not ? how can I tell ? HELP

Ladies help me out here. I feel like my husband smokes. Not sure if just weed or cigarettes or both. I've caught him twice with a joint, either in his pants or in the car. He tried denying it but then confessed that he did it Because he was stressed out. So that was like 7 months ago. Now I still have the feeling he still does it. 1 reason is: i keep finding lighters, 2: I've noticed in his bottom front teeth they have always been yellow and dirty looking (not too bad but it's there). 3: I read some messages of him asking his brother "where's the pipe or the lighter?" (This was last Thursday). The thing is I can't just confront him and ask him why he sent the message or why are his teeth like that or why is there always lighters around because my husband is a GREAT liar ! Yup he is. I need some advice on how to catch him. I have a strong feeling he smokes but he's sweared up and down he hasn't. I need more support to back up my accusations towards him because he will literally come up with anything to get out of saying the truth. What should I watch for ? Help me out ladies :( 
EDIT: it's more easy said than done. And as I read yalls suggestions I realized we're immature. And with that being said I know my husband is STILL going to lie about smoking, no matter what I do or say the only way to confront him is by actually seeing him do it or finding a cig. Someone said "my nose should be able to tell" but he'll still lie and say "I don't smell anything". Thanks anyway ladies.