Dog goes through screens

Question
We rescued our dog (35 lb cocker mix) a year and a half ago.  He has started going through screens to get to us and/or chase rabbits or squirrels.  Including out a second floor window onto narrow ledge!

He can't be contained in a small room or crate because he has anxiety attacks, he pees and pounds in crate, scratches up doors and pees if confined in a room.  He likes to look out window.  I switched screens from bottom to top of window and somehow he got himself up and out a small high window.  Just recently he went through screen window over the kitchen sink.  He had never been up on counter before.  I can see now why he may have been abandon.  We love him and we've got to find a solution we do not have AC we need to be able to open windows. He is on phenobarbital for seizures.

Answer
Treat him for separation anxiety. http://www.thegooddogjournal.com/2008/11/separation-anxiety.html
This may take awhile. Crate training is definitely a good idea http://www.thegooddogjournal.com/2008/11/crate-training-without-trauma.html

Also, it may help to teach him "wait at the door". I'm not 100% sure it'll help with windows, but it can't hurt:
Every time you take him through the door (which you should be for walks at least 2ce a day) have him sit and wait while you go through the door. If he gets up, say "nope" (not loud. You're not telling him he's bad you're telling him he got it wrong this time, no big deal. You could say "uh uh" or "oops" instead, some of my clients make a buzzer noise like you got it wrong on a game show.) close the door and step back in the house. Once you can get all the way out the door without him getting up and he's looking at you for direction, say "Okay, let's go" and let him through the door. Be prepared the first couple times you do this you may bound past you off the porch and pull you off behind him in his excitement. If you do this every time, he will eventually get the idea that he's not allowed to go through that door till you say so. He may generalize to windows, he may not.

Cocker Spaniels are prone to anxiety. These guys like rules and schedules to make them feel secure. You have to be a strong pack leader and set firm rules. http://www.thegooddogjournal.com/2009/02/whos-boss-establishing-pack-leadership.... I have a cocker mix as well and we've had a long road with him.