In beans I clean out the trap each day prior to starting and also when I hear one go in , you can hear them rattle around in there , makes lots of noise sometimes . I also have the stone retarder drum , get a few in there too . Have had the machine 6 seasons and haven't yet had one get to the rotor . As mentioned by the others you ""MUST ClEAN OUT "" the trap often , if it gets packed with dirt etc. the rocks will not fall into the trap they will go on through . I have a milk crate tied on the combine and in a season , 250 ac beans and 650 ac corn , I get it almost full of rocks that I take from the trap and what gets caught by the retarder drum . I have also picked up a few in corn , especially last year with all the mess we had here in NC Il . Again if you think there is a chance of rocks ClEAN IT OUT regularly it works . I would never have a machine without a rocktrap . JIM