walk it back in the dropouts.
tighten one side, pull back the other. Tighten that side, loosen up the other previously tightened side and pull that one back. rinse, repeat. Dont go crazy with the tightening though. When people walk back their axle they tend to overtighten. You really dont need your chain to be super tight. If you pull up on it you should get about an inch of movement.
EDIT: you sure as **** dont need chain tensioners.