Help - Outdoor Doggy Litter Box??

Hi everyone, do any of you have a building or construction background, or are you more inventive/creative than me??? Here's the challenge. I know there's an answer out there somewhere :)

I REALLY need to construct an outdoor doggy litter box. I found a couple of portable ones available online but I don't want something that involves using and having to change out kitty litter. Therein lies the dilemma...

We have two dogs (15 lbs and 55 lbs), who are together destroying the small (but slowly enlarging) corner of the yard where they have been trained to relieve themselves. Fortunately, we have a large enough side yard to place what I envision as a large doggy litter box, maybe 10 or 15 feet long by 5 feet wide. What I cannot find anywhere online are suggestions for how to build this masterpiece.

Here are my requirements...

It needs to be approximately 10 or 15 feet long x 5 feet wide. It will be on a patio with no protection from the elements. We live in Southern California so the weather is never extreme other than hard rain at times. It needs to be able to drain the urine w/out it building up, down in the box, in a way that makes it a smelly nuisance. I want to be able to rinse the box out thoroughly with the hose, without filling up the box.

What I need your help figuring out is what should be inside the box and how to allow for drainage, and what wood to use (or how to treat it) to withstand the elements. :confused:

A treated plywood bottom with railroad tie sides (or similar) would be fine, or I could use pine or similar for the sidewalls. Inside I would put pea gravel as the top layer for anti-splashing (while urinating) and easier #2 pickup. If I have to replace or add gravel once a year, so be it.

So far, my plan does not allow for drainage. Do I need to raise the box off the cement ground a couple inches, drill holes in the plywood bottom, and let it drain onto the cement, where I can rinse it weekly into the nearby patio drain? I'd want most of the urine to be absorbed and not freely flow out the bottom, at least until I need to rinse the pebbles. Do I need to do something more extravagant than that? How thick (deep) would the contents of the box be, and should there be a layer beneath the pea gravel and what should it consist of?

Any suggestions very much appreciated.

When this project is finished, we can re-carpet the downstairs. Holding off for now only because with our current system the dogs sometimes track in dirt and bud by stepping in the mud where their urine has killed the grass. :(

I don't think there is anything you can use that would allow for drainage and that your dogs won't track all over the house after it rains in the box. Do you know if you dog's would even use this new area after a good rain? Have you tried any lawn care suppliments or seeding in grass that is resistent to dog damage? Try your local lawn care store or hardware store. Also, what do you feed your dogs, it is possible that a reduced protein diet would help keep you lawn greener. I just use a sprinkler on the dog area of the yard to dilute the urine on the grass. http://www.yellowgrass.com/ Some people swear by the stuff on this website while others opt to treat the lawn not the dog.

If you are looking for an easy way out just make a raised standing frame of treated 2x4's with a cross braces in the center large enough to accomodate a small rigid plastic kiddie pool. Puncture the bottom of the pool for drainage and cut out a section (above the level of the filler). Fill the bottom with pea gravel. This way you can wash the gravel all the way to the bottom of the pool where the liquid waste will fall through the frame and with the standing frame you can wash underneath it. Rain will not stay in the pool and the doggies can do their thing in clean gravel.

If you already have a drain it may be worth considering an extra layer of concrete on that area of the patio with a slight gradient. This will channel liquid waste into the drain ( or into a small gully constructed with half pipes that slopes to the drain), allow thorough hosing and scrubbing of the concrete and easy poo pick up. A simple fence could then be erected around the area.