If for strengthening, then use the towel method. Don't stretch the penis, Just get erect and slowly push the erection down and kegel to push back. If you stretch and kegel, It's just working on the BC muscle and not the soft tissue of the penis. It's like when the penis retracts when you pull to quickly, it's the safety mechanism built into our body to protect the penis. You have to take the BC muscle out of it If stretching. It will slowly strengthen the BC muscle if you do that though, but regular kegels do the same.