Hmmm, it sounds like the threads in your BB (or the bolt) is stripped as well. The problem with constantly tightening the bolt is that it'll wear out the threads in the BB. Bolts, by their nature of being rolled, tend to have stronger threads than the hole that they're threaded into (which are simply cut by a tap, so no continuous grain at the surface of the metal). Over time, you'll strip out the threads in the BB axle and you'll need to replace the BB in order to keep the crankarms from loosening and falling off.

I don't know if you can run a bolt clear through the BB, the left & right side threads don't meet in the middle, so I doubt the threading is continuous.

What it comes down to is you have just ONE chance in the beginning to get the crank-arm bolt on correctly. After it comes off the first time, you tend to mangle up the hole in the crankarm and it'll never fit onto the bottom-bracket spindle perfectly after that. This leads to easier and easier loosening of the crank-arm bolt.

So on the 1st time install, do all you can to make sure the bolt stays put:

1. make sure threads on both bolt and spindle are clean and grease-free
2. use blue Loctite on the threads
3. use a star-lockwasher (split lockwashers don't work worth a cr@p!)
4. use a TORQUE WRENCH and tighten that bolt down towards the high-end of the manufacturer's specified torque

On Octalink cranks, that's about 35 lb*ft of torque. Using a puny 6" allen-key would require you to push on the end of it with 70 lbs of force! No way you're gonna do that without poking the allen-key through your hand. With a torque-wrench with 18" lever, all you need is just 23-lbs of force. Quite easily achieved with a 18" handle on the torque-wrench.