When I originally installed my X-arcade into the cabinet, it stayed in place nicely due to how snug it fit into the cabinet slot. However, I discovered that during two-player games, the controller could slide to one side and essentially fall out. This wasn't the best situation. The following simple solution is one I've told a number of visitors when questioned. I figured it was time to throw a page up showing the 'fix.'
First buy a piece of kraft board, 1/2"x1-1/2"x30". Cut it to exactly 20" long, which is the interior width of your cabinet. Obviously, if you've altered my plans, this length will need to be adjusted.
Paint it black, if you wish, and let it dry. Then flip your X-arcade controller over and measure back about an inch from the rear. Find the center left-to-right and simply screw the board in place with a screw at least 1" long. One screw on either side will be sufficient. This won’t hurt your controller in the least.
A side view is shown below.
Now, once you press the controller snugly back into your cabinet, it should
stay there. The backing board will keep it from shifting either way.
Hopefully this helps.