[Discussion] A dogs backyard design

I'm designing 2 bed 2.5 bath townhome 20'x20' backyards in Wisc on north side of property and I have a few questions. I'm assuming our tenants want fenced backyard space but don't want to do maintenance and don't want to pay extra to install a gate and have a landscaper cut grass. So does your dog require grass to go potty? How much grass would you be able to maintain with a grass shears or weed wacker, about 10 sq ft like a porch potty size? I'd have most of the rest of back yard as pavers and raised planters for small garden maybe a little tree and room for a hammock or kids toys. Does your dog go potty in gravel?