Ooooooohhhhhh!  Cool idea.  Peanut butter balls.  

8 hours ago, Al B said:

I've experienced their persistence. Just wondered if paint might deter the chewing.

 

Al, an arsenic laced paint might stop them - wouldn't deter them, but would eventually stop them!

I used to sell a metal guard to put on the front.  Not 100% effective, but helpful.

 

You can find large bushings at Ace also, you need to get the right size (1 1/2" ID for bluebirds) and drill screw holes in them.  And also pilot holes in the birdhouse as you are drilling close to the edge.

 

Shooting them is out of the question here. First, my wife won't let it happen. Second, the law doesn't allow gunfire within the neighborhood.  Third, my neighbor, who lives on a side street from my street has a back yard that abuts my back yard is a policeman. Can't use poison peanut butter balls because of the neighbors cats. They don't help at all, except for catching an occasional chipmunk. 

Dang, Al.  You are on real lock down.  I use a pellet gun.  I also look around the neighborhood to see who is home.  Then I wait until they get on the inside of the tree toward me and nail them to it.  It is rather quiet.  Oh, what am I talking about.  I forgot you have to live with your wife.  Sorry.  It seems you are in a real jam, or pickle.  But, some D-con pellets placed outside that is not visible to others works very well.