Alstack,

Rubber bands are the preferred method for holding wing on trainers. The mistake comes from putting to many on the wing. It all depends on the weight of your bird, but for a forty sized trainer, I would only use 8. For a sixty sized trainer, use 10 bands. I fly a combat bird with 8 and I have never come apart in the air because of the rubber bands breaking. Most of the guys at my field will tell you to use more than this for strength, but I routinely have 160 mph mid-air collisions that result in no damage. When you hit the ground, something has to give because the ground will not.

Bob