Sun shade for in the car

A while back I bought a sun shade for the car rear window. It has those little suction pads to keep it up. But whatever I do, it only stays up for a few seconds.
How can I get those pads to stay stuck to the window?
Is anyone else using these shades, and how do you keep them in place?

It's really annoying, especially with the sun being so low in winter time, and poor Mika is lying there with her face in the sun

Ah, I got those window socks for the side windows (didn't know you call them that lol), but you can't do that for the rear window. I'll try the wetting again, I thought I had tried that, but maybe I only thought I had .