GPS suction cup adherence to windshield

Some suction cups are much better than others. But a clean suction cup and a clean glass is your best hope.

If a GPS, I much prefer the beanbag type dash mount to a suction cup mount. Down low out of line of vision, and easy to move to floor out of sight when vehicle is parked.

Johno2 is correct. Make sure you are cleaning the windshield..alcohol.

I have one of these. It has not moved in over a year. Very solid.

Suction Cup Mount...LINK

Cleaning good with alcohol wipes helps somewhat, then clean it each time you remove and replace. The changing temps will harden the seal, and it does need to be removed and reset often.
Also, be sure and clean the little circle off the glass whenever you remove and store the GPS. The little circle is a sure indication to everyone that you have a valuable GPS in the vehicle. You could end up with a lot of broken glass even with the GPS hidden.

Ditch the suction cup. They age too fast sitting on the glass and will not hold for very long, even if conditions are perfect. I have one spot under the windshield glass where I have permanently adhered a pad of 3M "Hook and Loop". This is similar to Velcro in concept but is much stronger. The hooks and loops have a very positive hold. I use this pad for GPS antenna or anything else I want up there. I have door-mounted audio tweeters, they are also adhered with this material and they stay in place through many door slams.

Please dont super glue anything to your windshield. There are PAGES and PAGES of various GPS type car mounts on Ebay. Find an alternative to the suction cup if its not working for you.