Help with idea: Alert trigger when passing boundary

Hello all,

I have a little dog that is somehow getting outside of the fence that is completely chicken wired in. I don’t want to use an electric collar, but want to put something on her small dog collar such that if she passes align, a notification is triggered. Something that is RF that sends some signal when it crosses and electrical wire under the ground that goes around the perimeter of the fence? I am really open to ideas, and I’m very new to this stuff, but this little project would be fun to learn and help me keep track of my dog.