Alkaline PH. If you are worried about stress fracture - this is due to vitamin d deficiency and if you take vitamin d and maintain alkaline pH to prevent osteoporosis. You also want to make sure you with the help of your doctor how your bone scan is whether you have lost bone density which increases your chance of fracture. If you just need cushion then you can use dermasaver products which provides padding.
Nothing. If we new how to prevent injuries I could look for another line of work. If you are nutritionally sound and do not have osteopenia (low bone density) all you can do is exercise caution with high risk activites and live out your life.