What can I put outside my bedroom window?

Our main bedroom and my little boys' bedroom windows are quite low to the ground and both look out to the back yard. We have 2 dogs and they are making the windows filthy - and I have caught one of them ing his leg to pee right on the window ledge outside my little boys room - yuk! Need an idea for something we can purchase or place out side in front of the windows, but would still also like to be able to see out into the yard....