I'm trying to trade a system that shorts US stocks at the open. These are all stocks with decent trading volumes, but for some reason IB keeps rejecting my trades b/c it doesn't have enough inventory to execute the short. I'm looking for two kinds of recommendations: 1. Is there another broker who is better at executing shorts than IB - i.e. keeps more small caps on hand? OR 2. Can someone recommend a piece of software that will keep trying (submitting) the short order throughout the day until it executes? Right now, I have to sit there at the TWS and keep clicking "transmit" throughout the day - there has to be a better way. Thanks