The easiest and safest way for a squirmy chin is making a "burrito" with a towel. Wrap your chin up in a towel, not too tight, like a burrito. This should help you restrain him. Then try performing the check while he is restrained in the towel. It's easier with two people; one to hold the chinnie while he is wrapped up, and the other to perform the hair ring check. KY jelly works very well to help lubricate the penis and make it easier to extract and retract.