Mine is thinner, 20 mil I think it was, 19x25 for $213 off ebay.
For rock, something you might want to try, I've told lots of people this, unless you are somewhere in the country where there just isn't any rock, pull up to any farm house in the area and knock on the door and introduce yourself.
Almost every single farmer in my area has a pile of rock somewhere that they have hit with the tractor while plowing, picked up and tossed into a pile. They don't post it on craigslist because they can't comprehend why anyone in their right mind would want a big ol pile of field rock. It's just junk to them!!
I got mine from my own aunt and uncle, and uncle Al was amazed that anyone would want anything to do with those rocks, even after I told him what I was doing, he said "well there's a pile right out there take as much as you want, i'll be glad to see it gone, but I'm sure i'll find more"
As far as the fence, I don't want to fence in the entire front yard, and the rock bed area will just be a small area in the yard right in front of the deck, could do a small fence around it... but nothing that would keep a dog out. It'll be probably next year before i do anymore yard work, as i just rebuilt the backyard pond this year and put the fence around it. So I've got more time to brainstorm.