Will a robot mower drive off a ledge or into a pond?

It shouldn't, as long as the boundary is set up properly, but no mower is designed to spot a drop or water by itself reliably, so the boundary is what protects it.

Wired mowers stay inside the perimeter wire. Manufacturers' installation instructions give minimum distances to lay the wire from ponds, drops and walls, and following them is what keeps the mower on the lawn. Many also recommend a physical barrier around a pond.

Wire-free mowers stay inside the boundary you draw in the app. RTK mowers are accurate to a few centimetres in open ground, but accuracy can wander near trees and buildings, and cameras and LiDAR are good at seeing walls and objects, not necessarily the edge of a sunken pond or retaining wall. Draw the map with a margin from any hazard, mark ponds and flower beds as no-go zones, and watch the first few runs.

Watch for three things in particular:

• Lawns that end at a drop such as a retaining wall or steps. Leave a buffer, or fit edging or a low fence.
• Slopes that run down to water. Wet grass can let a mower slide past where it meant to stop.
• Boundary slope limits. Some manufacturers set a lower slope limit at the edge of the map than on the lawn itself. Segway Navimow's manual for the i Series limits boundary slopes to 10%, for example.

For layout advice, see our guide to installing a robot mower.