Turtling - that thing where your dick shrinks into itself like a scared turtle and gets stuck in the tube - seems to happen whenever you have a close fitting chastity device. (Long forum thread here.) I have - I think - stumbled on a fix. The short version is, have the C ring or end of the tube part (start of the head bulb) begin a few mm earlier (Wikipedia diagram marked up by me, hope it's not offensive). The position is roughly just before the root of the foreskin or foreskin scars: (Black shows parts of my "Saint" cage. Same logic applies to other designs) This way, the C ring (or tube end) has a good purchase on the "corpus cavernosum", i.e. the meaty part of the penis. When the penis turtles, it's rearing up with the C ring behind the head and doesn't retreat or stick. I've written up the device incorporating this fix on my blog. But the above pretty much covers what I've discovered. My suggestion would be, not to buy a device that's shorter than you think you need, but to go for one with an exaggerated head section, or at least to pay attention to those measurements.