Please Help! My German Shepherd jumps up and bites (and breaks) the top of my 6 foot fence

I have a three year old German Shepard (that I have had for about 2 1/2 years) that jumps up and bites the top of our six foot fence (we just replaced one side.

The neighbors paid for half and are not happy that our dog is eating the top).





We tried an invisible fence which did the trick for a few months but then he just started to ignore it.

Radar (our GS) loves to chase birds and has made that his self-proclaimed job. Could he be trying to get to the birds?