Now be advised that this will be an experiment. Your anatomy is unique to you, and flesh tunnels vary. You may need to try a few, and you may find challenges. The key to success will be the same on Thomas Edison used. Keep trying till it works!
Look for tunnels which look like spools on which sewing threads comes packed. They should have a raised edge on both sides which will tend to lock the end of your foreskin into the recess area of the spool. However, you don't want too much of a raised edge in order not not irritate. Making sense so far?