"Walking" circulation pump

[Retired_AF]

I have 3 circulation pumps in my 90 gallon tank. One of them absolutely refuses to stay in place and migrates towards the back of the tank. I have let up on the tension from the cord and made sure the suction cups were clean when I moved it back yesterday, but today I found it almost to the back of the tank. This makes the water flow hit the rocks, blowing the sand all over the place and makes a general mess of that part of the tank. Any ideas on how to stop this thing from wandering around? I am so close to finishing the fishless cycling process and this is driving me nuts...

 

[Hondatek]

The only two things I can think of are 1. Replace with a powerhead that uses magnets instead of suction cups .2 silicon the suction cups to the glass .

 

[54seaweed]

I crazy glued the suction cups they stay put now
did it during water change so I had dry surface