If it's nogi, get your dominant arm free and drive it across their face hard so their head is completely turned. Grab that hand with the other and pull back...neck crank finish...if they lift their chin RNC or if you feel like being a little nicer pull up instead of back then quickly slide the arm down to the open neck.
If it's gi, neckcranks aren't allowed, and you can't get a collar grip deep...you'll probably want to trap an arm. Bother him until he grabs an arm then feed that arm back and hook your leg over it. Hold his other arm with one hand and work the other hand under his chin and get a deep grip. Work chokes.
Had the same problem, this stuff works...now I just don't seem to get the back as much.