Hi, Chris,
I haven't seen a diagram or photo of a limiting strap. Usually the shock absorber is what limits the lower position of the suspension, so my guess is that the BEST way to do it would be to use a shock and spring that are shorter than stock and is at maximum length when the wheel is at 0 degrees camber.
A steel cable or strong leather could be used as a strap with stock springs, but then it would have to be strong enough to hold the spring in compression. Using a shorter spring would be better, as then the strap would just have to be strong enough to hold the actual weight of the suspension arm, brake, wheel, and tire, which isn't that much.
I don't know the details of how it's done and what material will be used
Maybe when my car gets here it will have a strap and I can photograph it.
Jim