I take it you have plenty of room at the end of the saw guides and can pull the lengths out, the end of my saw guides are up against a wall. I don't think it would even work to hold my short lengths.
I was going to suggest hydraulic opening and closing gates for catching nervous cattle and tailgating BMW’s!Yes that's already been thought of . I used to use a rope that closed the small pedestrian type gate behind them and I'd hold the rope like a trawler line until I could get to the catch.
With this I may be in the Treibewagen so again closing the gate behind them