i used to have one of those u lock holders, decided to take it off my bike for a very clean look (currently have coaster brake, no hand brakes), now if i take the lock with me, it goes on the handlebars or in my backpack if I am carrying one. the over handlebars will make the lock bump and rattle if i am on the road with many bumps and potholes. the backpack location, not possible if i am not wearing my bag. i used to have it on the seat tube with a ulock holder, decided against that since it throws the look of the cruiser bike off (i ride a cruiser bike). so where else can i put the u lock?
Do you go to different places? If you just go back and forth to one place you can lock it to whatever you lock your bike on and nobody in the right mind would steal it. They would have to break it, making stealing it useless. It wont move and it will always be there waiting for you when you get back.