It’s completely dog safe, has good drainage, and can be customized to whatever size you want.
Artificial grass has the advantage of not bleaching from dog pee, and the drainage is still good. However, the surface temperature can be 20 degrees F higher than real grass in full sun, which isn’t pleasant for your dog.
It’s got good drainage, is easy to clean, and won’t smell like artificial grass. You could use it in any outdoor space, provided you’ve got somewhere to hose the water down.
Mulch can be a good option for a dog potty because it’s super absorbent, meaning it’s easy to dispose of the soiled material.
Sand is a good option for a dog potty if it’s built in a covered area. Plenty of dogs like digging in the sand, so it can give them a bit more enjoyment than other materials.