Tanks for the idea
If I was designing an autonomous vehicle to go motoring around the garden hacking down plants, grass and anything else that got in its way, I'd be drawn to a RC model tank as the basic platform. Apart from the sheer "cool" of a tracked vehicle, I reckon that when you scale up the natural contours of a less than perfectly flat lawn, then that's a reasonable match for something designed to drive over battlefield terrain.
Depending on the amount of ground clearance, there should be scope to mount a rotating-wizzy thing under the chassis; safe for prying fingers, nosy cats and slow-moving grannies. There's also the long-term possibility of doing something with the gun turret. I'd suggest using it as a means of delivering systemic weedkiller to dandelions in the path of the all-conquering garden-force.