Country to Town Potty Training

[tai]

Hi -
I'm new to this site and we are moving from the country with our two dogs (Golden Reteiver - 7 years old male and German Shepard mix-10 year female) into town with about 80 x 100 feet of yard. Currently they are both inside at night and outside during the day where they have the run of the acreage We are planning on putting up an invisable fence to keep them in our yard. (there also is a great park about 3 blocks away where we can bring them so they can really run and exercise My concern is how can I train them to go potty in one place in the yard so I don't end up with brown spots all over the yard ? Both are 100% housebroken so that is not a problem, I just never have cared where they go outside before now. Any help or ideas would be appreciated!!

Tai