I was tired of my rear floor mats shifting around. After an exhaustive web search (not that I searched the whole web, just that I'm exhausted), I found and ordered this product: Mat-Loc Clips from GGBailey.

https://www.ggbailey.com/ggbailey/pa...ar-accessories

I also found this:
Product Listing - csa023
but didn't choose it for two reasons:
1. They don't appear to be taking orders at this time
2. The pins might be hard to insert and still have the clip close to the rear of the footwell.

Since the Mat-Loc pins are oriented sideways, it should be easy to get them all the way back in the footwell. I'll post again to let you know how I like them when I get them installed.