Thank you very much for your critique. This is not the picture I completely hoped for, but I'm using this point & shoot digital camera so I haven't quite worked out exposure. As far as composition is concerned, you are correct in your assessment of Lester's energy; it's not easy to get him to sit still for very long. I snap the shot when I can. Thank you again.
Lester looks like a very happy dog - as he should be sitting in such a field. I find it difficult to get good photos of our dog b/c she is always so focused on what is going on and that is usually not where I'd like her to look. I'm going to guess that Lester and his friend are high energy type dogs as well.
Very good Depth of field and good choice of background. With Lester close to the left of the frame and looking off camera, my impression is that he's run all the way up the hill, but now is sitting down. I more expected him to be to the right looking into the frame with the bridge in the background. Or still running out of the frame.
There are some techical details on the shot that may be only related to this small sized or may be on the original. The horizon looks tilted to me (but then Lester wouldn't be straight?). The day must have been really bright, Lesters highlights are blown out, but there isn't enough light on the shadowed side. Black dogs are HARD to shoot on bright sunny days. I've found on camera flash usually helps, as do overcast days, shadows, and if you have an assistant a reflector.