Dear Christopher Cat: Kojak, my diabetic grandcat, refuses to remain indoors, endlessly meowing and scratching the door until someone lets him out. Then he escapes from the backyard by digging under the fence.

He can remove any collar or harness ever designed, so he needs an implantable GPS microchip to track him. Can you recommend a good one?

Christopher Responds: To the best of my knowledge, the perfect microchip tracker hasn’t been invented yet, partly because the battery life would be too short.

But I have a better suggestion: a cat fence that even Kojak can’t get through.

Most cat fences are made of a black, chew-resistant, polypropylene mesh that blends into the landscape. The fence extends about six inches underground, and the top slants or pivots inward, so cats can’t dig under or climb over the fence.

These fences can be added to existing fences or walls, or they can be installed as free-standing fences. You also can add gates and barriers that prevent the cat from escaping by climbing a tree.

The fence kits are designed to be installed by the homeowner or another handy person. Visit purrfectfence.com, kittyfence.com, catfencein.com and catfence.com to see several options.