On mine i took the spikes off the plate and put Smooth-on metal set epoxy in the holes on the spikes and a tiny bit on the spike surface that touches the plate, and screwed them back on. Wiped away any excess after that and let it set up.
I used small wood screws with a touch of superglue, and just screwed them on to the boot, keeping the plate in line with the top edge of the sole. I put a dab of the metalset epoxy on the plate ends to keep it from tilting up and down and thats it. I did that for both pairs of boots i have and they never came loose or moved.