I tried this and it didn't work so well, learn from my mistake.You could use the gravel in various places, such as around the outside of your (human) house, or the coop/run, to discourage pests from digging under.
Someone in the past stupidly mixed common "salt & pepper" river gravel into our crushed stone gravel driveway, it's slippery and doesn't match, so I've been trying to get rid of it in various projects around the property. I was able to use a lot of it in my coop's cinder block foundation, which was great because it's fully buried. But then I thought I could use some around the perimeter of my chicken areas, on top of the HC skirting, to keep animals from digging down to it --- hahahahaha yeah right, they just scattered the rock like it was dirt and now it's real fun to mow that section of the yard. My chickens easily dig up larger rocks, such as 4-6" cobble stones and all the firewood chunks I place around the perimeter of my extended run to keep them from digging on the inside fence edge, they just kick those around and get to the worms/bugs hiding underneath like it's a game.