Puncher Guides Breaking

So I made a puncher for my robot following the basic design of a linear slide sliding on the inner linear motion guide pieces with rubber bands pulling them forward. These rubber bands are connected to a cut piece of metal nylocked to the slide. However, today I had to completely disassemble the launcher as a nylock holding the piece holding the rubber bands in the rear of the slide damaged the rear guide enough that it got lodged inside. Is there any recommended way to fix this or is there a flaw in my design?

Pictures would help, but as i am imagining it, you should probably add another mechanical stop that stops the slide before the nylock hits the slide, such as a c channel hitting the back of the gearbox, essentially, 1 pice of metal on the stationary part that hits a piece of metal on the slide, such that the metal htting each other is the physical max the puncher can go forward, so nothing else hits anything.