Get 4 of these u-clamps. These I already had, but they cost $1.09 at my local hardware store.

The two front holes on the brake-side guard line up, but the side hole doesn't, so here's where the u clamp plate goes

This lines the holes perfectly and adds strengh to the side of the guard.
The non brake side needs a plate on the front as well since the fork only has one hole in front. The hole closest to the spokes mounts up to the guard fine, so slip the u clamp plate under that bolt which allows the other hole to be mounted with a bolt as well.

Mount the side hole with the other clamp plate and you're finished.
