rendering on top of other things

i know a trick that makes rendering on top of other 3d things, it goes like this: make a new camera to be child of master camera (i made transform of the master and child the same)

child camera clear flags: depth only culling mask : drawFront (make this layer)

add objects you want to render on top of other things to this layer

this however doesnt solve the issue that it does not render on top of GUI. so i have a line (rendered in OnPostRender with GL class) that isnt rendering on top of GUI is there a trick to do that?

any help appreciated!