I was having this same problem with Toto. He has a pee string, and that wasn't the problem. The problem was his long hair from his saddle (back) hanging down in front of the stream and him getting dirty.
Here is my thread on that. I ended up using hairdresser's clips to clip his hair out the way before we go out and it has helped. I keep the clips on the end of his leash so I remember to use them every time. It has helped a lot.
http://www.yorkietalk.com/forums/gen...u-kristen.html