you can use
pvc pipe to build a skeleton then attach the
lr to the pipe,the pipe is the basic shape and also holds it all together,If you have put the pipework together correctly you can also drill small1/8" holes into the pipe and attach you return pump to it so you have a good flow around the back of your
LR otherwise I have just used putty to hold all of my main base rock in place and then gradually added smaller pieces to build up the aquascape.