I had the same problem with my Navigator and 2 main drain covers. So I modified the drain covers with a 4" PVC cap that I cut down to make shorter, drilled a couple holes in the sides of the cap so I could zip tie the cap to the top of the cover. This makes a little dome on the top of the drain cover and prevents the Navigator from climbing on top of the drain.
My Navigator was also falling over when the suction hose went in front of a return jet. The water coming out of the return jet was pushing the hose and causing the Navigator to fall over. When I use the Navigator I aim the return jets at the ends of the pool and down a little. This helps keep the hose away from the return jets.