DIY disc guards

I'm interested, but not sure how covering the brake will work (don't different brakes stick out different amounts?) or what it's going to mount too (the only point that you can be certain of existing on a disk brake bike is the holes the caliper mounts too right? But that's going to make clearing the caliper even harder isn't it?)?

Yeah I was thinking it would probably have to be on the caliper bolts, but then you'd have to take the caliper off if you wanted to remove the guard.
The design obviously won't be straight forward, but I wanted to see if it was possible to get these made first.