While cats don't seem to like the feel of rubber mulch under their paws, dogs are just fine with it, and rubber mulch is great for dog runs and kennels. Unlike other surfaces which might absorb urine and other smells, rubber mulch can't, and it can be disinfected with something with a better and more desirable scent. It's probably a good idea if you are installation a playset with rubber mulch safety surface or a dog run / kennel, not to choose the color brown, if you have one of more dogs (for obvious reasons involving visibility).
Because dogs like to often kick and scratch the ground with their hind paws after their done doing their doo, it's a good idea to have a 3" thickness that can easily be evened out when cleaned. It's also good to include sub-base drainage, allowing the capability to clean & disinfect it, and have the best opportunity to eliminate or minimize unwanted odors. A good solution is picking up a bottle of concentrated organic disinfectant at your local janitorial supply, that has your favorite scent (lemon, pine, lavender, etc.), mixing some up in a garden sprayer to apply, then hosing it off before it dries.
In addition to having a cleaner area for your dog(s), it's also healthier because the pathogens all animals have within their waste can be eliminated (pun intended), and not tracked around to possibly infect other animals or people. Dog waste pathogens are a very real hazard and the primary reason for beach closures after any decent amount of rainfall that results in urban run-off that likely contains these types of particulates. The founder's sister knew someone years ago who went surfing off a local pier a couple of days after heavy rainfall (not a good idea), resulting in mandatory heart replacement surgery at age 19, with no family history of heart disease, and yet severely damaged by exposure to even at that relatively few parts per million. Diseases and parasites passed from animals to humans are referred to as zoonotic, as are most epidemics like what we've all been dealing with for years.