Dog Potty Areas?

I want to do a fenced potty area in our yard this spring. Has anyone else done this? How big did you make it? What is the best footing?

A lot of people in my area take a 6x6 kennel, remove a wall, and put it up against the side of the house that has a convenient door. They don't put any flooring in or anything, just the grass that's already there.

I've seen just small gated off areas with just dirt/grass.

or this kind of giant dog litterbox thing

and use gravel
http://www.welcomepup.com/blog/how-to-build-an-outdoor-dog-potty-are/

Sort of. My backyard is massive, so I sectioned part of it off. The front part of the backyard is the "potty yard" and there is a chain link fence that separates it from the rest of the yard, which is the "big yard." If I just let them out to potty, they're in the potty yard. They go in the "big yard" when it's time to really run around and play, practice agility, et cetera.

It serves two functions: one, I don't have to worry so much about random poops underfoot when we're practicing agility. Two... Payton will not be nearly a full football field length away from me barking at a squirrel at 1AM in the morning when I'm at the door in my underwear screaming "YOU BAD DOG GET BACK HERE!"
The "potty yard" is only maybe, I don't know, forty feet? And the big yard is the rest. So it's not really "small" exactly.

Here's some photos, these are actually before/after photos to show work we did but you can see the fence and stuff here:

We separate a section that is easily accessible from a door everywhere we live. We haven't done it yet here because we moved in a month ago and there is 3 feet of snow...spring is going to suck.

We don't have a fenced area, but I make Watson pee on mulch areas near the door so it doesn't kill the grass. My husband is going to add this tall iron sculpture thingy left by the previous owners, so he has a vertical surface to aim for that isn't a bush. I'm sure gravel would work well, but mulch is a little prettier if you want to incorporate it into your existing garden better.

We have an old Xpen near the corner of the house with aspen chips in it. It was supposed to only be until Caleb was big enough to go out on the overhead tie out, but it worked so well that we've left it up. Eventually we'd like to move it to the end of the porch, but that won't be until we can replace the windows there, and put in a doggie door. I'll see if I can find a picture of it.

We have a temporary one right around the deck...it's about 30 x 60? But the deck takes up the middle of it, so it's really a U-shape. Just grass right now.

Planning to put in a permanent solution this year, that looks nicer. Thinking about using rock for the potty area, but still deciding...