... that is, if people are doing this kind of thing to gum up the works for their competition, one answer is to assess a very small fee per trade, less than a penny. This would be completely negligible to a normal investor, but could be quite expensive to those trying to saturate the system for the benefit of their trading algorithm. Market-makers like Goldman Sachs would also wind up paying significant amounts, but given their privileged position which basically gives them a license to print money it's only fair. The fees collected could go into an insurance fund to help cover the next financial meltdown, and if it slows down trading a bit, that may well be a good thing. Complex nonlinear systems have a tendency to go unstable, and damping is one way of decreasing this possibility.