Is there a training aid for foosball players?
There's a rollover training system thingy that I've heard isn't very useful.
I _have_ found it quite useful to put a cutout man (see below) on the opposing 5-bar just inside the 2nd man out, and a cut-off bumper on the near wall of the same rod. Then rubber-band the rod against the wall and practice passing.
IE, something like:
bBM----mM-----M------M------M-----
The B are bumpers, you've now got an extra one on there (the lower-case b). And the lower-case m is the cutout man.
The point of doing this is so that you have space to pass a wall pass because of the extra bumper, but the extra man is still blocking where the rod would normally block if it were against the wall (so that you don't get in the habit of passing your lane pass where the 2nd man can stop it).
A "cutout man" is just a man where you've filed out an opening on the back of the man so that you can pop him onto the rod. (I then put rubber bands around his ankle and the adjoining man's, and around his head and the adjoining man's). Just look at the man from the side, so you're looking throught the hole where he fits on the rod, and cut out part of that cylinder so that you can pop him on the rod.
Other than that, rod locks can be useful but I usually find that I want to change the defense often enough that I don't bother with the locks.