Police academy?

I was accepted into the air force.. When im done serving my term i want to be a police officer. I have experimented with marijuana but have no legal record of it. I hear they do polygraphs when they hire you though and that is a question thats probably going to come up.. Fooling a lie tester is virtually impossible so if i admit to that can i be a cop? dont they prefer people with military experience? what kind of questions are asked? will they allow me to be a cop?