Siliconed the sucker to a magnet, huh? Hey, I like that.
Normally what I do is epoxy the **** things to a long piece of plexi, and then shove the plexi in the gravel. The force of the powerhead blowing water keeps it pinned against the glass. I've actually suspended the things from the top of my tanks this way if I want them to point straight down.
You'd think the egg-heads that build these contraptions could build a long, U-shaped black piece of plexi that could simply hang over the side of your tank and yet allow you to adjust the depth of the powerhead down to a reasonable amount. Instead we get suction cups that insure you'll become an expert at digging sand out of the impellar with a pair of pliars when they fall bottom first into the substrate.