Once you reach your target, it must be cemented and by this I mean to simply make it permanent so it becomes new growth. Once it has become new growth, which takes around 4-8 months in my experience for this to occur, when you than cease all Penis Enlargement the size wont shrink back, but remain its new size.
I have had gaps of over 2 years with no Penis Enlargement and kept every single monster inch and that's because all the growth I had, was permanent. Guys that take 'gap years' and lose size, never had it in the first place.
I would suggest though that you keep yourself fresh at this, even when a target is reached by simply doing it once a week for general health of the penis. You'll also find I can guarantee you now, that once you start seeing gains you wont wanna see them stop.