C&C per req:
1. I think it's a start, but a start with a way to go. There are a few technical issues. First the image leans drastically to the left; always try and hold your camera level and square. Line up the grid lines with fixed points on the horizon. Next, the sky and water suffer from blown highlights. This is a bit of a challenge to deal with at mid-day, BUT the use of a polarizing filter will help, especially with the water. I honestly can't be sure if you've nailed the focus on the dog or not.
On the artistic side, something coming toward us is always more interesting than something going away. Get out in front and get the shot. As well, there's a LOT of unused space not contributing to the overall image.
2. This is a really neat image. I would consider cropping about the bottom 1/4 - 1/3 off just to feature the rainbow more prominently.
Just my $00.02 worth - your mileage may vary.
~John