Need help with Lay down command.

I have 2 Pitties both male and 2 years old. Currently Im trying the method of having them sit and follow the treat in my hand until they are laying down and using a clicker and saying lay down as the complete the movement. Then rewarding with the treat by opening my hand. Both of them have been stuck at the stage of only laying down after following a treat for a few days. How do I progress to them laying down while not guided by a treat, so I can reward that desired behavior. Should I keep doing what I'm doing or try the leg bridge or capture methods?