You can buy this to expand the range:

The Wireless Fence Transmitter can be used to expand the limits of your existing IF-300 The Wireless Fence Transmitter can be used to expand the limits of your existing IF-300 PetSafe Wireless Instant Fence Pet Containment System. You can use this additional transmitter to increase the size of your containment area. This creates multiple intersecting circles. The two transmitters would create a boundary in a shape similar to the MasterCard logo. The signal is canceled where the circles intersect, allowing the pet access to the entire area. The transmitters can be located a maximum of 150 feet apart and each transmitter must be in an enclosed area.This transmitter is compatible only with the PetSafe Wireless Fence Receiver (IF-275).

Looks like the price might make the in ground wire one worth the effort.

Did you ever solve this? Bourbon has the same issue and I am wondering if you solved the problem. We have the same fence. And I have lots of fence

A hot wire extended out and up at an angle from your fence so that if he touches it it will shock him. you can buy the wire and the regulator from lowes or homedepot. I used it on our Denai when she became an escape artist. she got shocked twice and never escaped again from the fence. She just bolted out the front door when we opened it for friends.

We bought our hotwire supplies on Amazon, btw.