What I don't love is that even with a straight ruler, I have mange to cut circles (I exaggerate but, not by much) because the ruler was sliding so much. So I tried the very thin adhesive donut types but, they wore off after a few months.
Then I tried the Invisigrip cling but that just wasn't enough.
In both cases, the product did keep the ruler from slipping when I was cutting one or two layers of (mostly quilting cotton and light to medium apparel) fabric but when I added more layers where the template may be just above the cutting mat, the ruler may still move or even the fabric because I was using more pressure on the ruler and on the rotary cutter.
Don't peel off the Invisigrip though, there's still a good use for it on your ruler...I then saw the clear door bumpers or furniture feet. Those were just too thick. Then I happend to find bumpers that were thinner but, of course i used them all, threw away the packaging which meant they were perfect!
It took me a little while to find them again but, I did and this time I noted the thickness. They are 1.5mm thick. Dritz makes them and I found some at Joann's Fabric store for around $5.50 for 24.
Then I searched for larger packs by entering "Clear Self-Adhesive Flat Rubber Feet 1.5mm" and found them on Amazon! Usually in 100 to 128 packs for around $10. I usually make sure the seller is showing an image of a foot in a side view next to something showing relative size.
The ones I really like are round and flat like these...
In summary, the 1.5mm feet work well with more layers because the feet sink into the fabric. The Invisigrip worked will up to three or four layers depending on the fabric thickness.