How old is this dog?
I would be SO careful with a 90lb dog and the impact this could have. I think frisbee is fine, so long as you know how to throw correctly, and use caution with windy conditions. Also, keep him VERY lean, he needs to be competition weight if you are going to expect this type of impact exercise on a dog this size.
If you can throw on a straight plane, lower to the ground so he runs ahead and can grab it out of the air without a lot of jumping, then frisbee can continue.
I also got this book:
I taught a few tricks already, like the butterfly throw, jumping over legs etc. The size of your dog is going to be the biggest impediment to this type of training. The larger the dog, the harder this is on their bodies.