A simpler deterrent would be to linearly increase cost of the next domain you buy. This is the opposite of bulk discounts, and should make squatting unfeasible (at least not in large numbers).
How about because they paid for 200x .coms?
BTW, for you and some others here:
Domain squatting is when someone registers domains in the hope that trademark owners will shell out cash to get the domains.
Domain squatting is not when someone simply registers domains you happen to like and wish you owned instead.