I think one way to prevent dumping is to reward bounty hunters either through eth or btc. Also, they should not offer discounts so as to prevent dumping by investors. They would want to sell at ico price or even higher instead.
I have seen projects do this in the past such as with Qtum and it seemed to work well for them. Another method to help reduce dumping would be to allocate only a small percentage to bounties like 1% of the total coins and maybe distribute them in portions.