On my bmx bike i cannot make the chain tight.?

I pull it back and try to keep it there but tightening is to difficult as the axel spins. So then i took it to the bike shop and he made it tight. But 1 of the new axel nuts he put on was striped out (w t f hear wat im saying?) so then the rear wheel turned into the frame and i couldn't peddle . is there any tips to making it taut? Use washers? do Chain tensioners work? Ive tryed everything and the chain never gets tight and when im doing jumps and it derails it sucks so much. O and the frame is a bit tweaked.

Odyssey P.A.C.T.

The chain tensioners sound like a great solution to the problem. Quite a few BMX/Freestyle bikes already come with them stock.

I think a chain tensioner might help you,but don't buy the cheapest.
If your a hard rider I suggest using two nuts,one to set it right and another to lock it,that is if enough threaded axle is there to do so.
Please keep in mind that not all front rings are actually truly round.
I was asked,many a time to put a 'chop' in a chain tension.This means keeping the chain tight when the ring is at its peak[so it is tighter]. This was to stop the crank from moving freely when crazy tricks are tried.
It really sucks when your crank continues to rotate after your feet have left the peddles.
The chop is to stop the movement[freely] so you know where your peddles are for a landing.
The 'chop' does mean your front ring and chain will wear [wear out]more.

I hope this can be of some help to you