Is that the second wheel bearing that's breaking down? That's rather uncommon.

In any case, have your mechanic replace the bearing, and don't forget to have him replace the seal as well, and lube the bearing properly with the correct grease. A faulty seal will drastically shorten a bearing's lifetime because soil particles like sand are very abrasive.

Roland --- Mark was thinking the same thing --- that it's odd two bearings would break down in fast succession. But maybe this is just the time they're likely to go since they're all the same age and have dealt with the same rough wear?

The seal was what fell off the second time and made Mark stop driving until we get the wheel fixed. My job this morning is to hunt it down along the floodplain as I walk Lucy.

What I suspect as that your off-road use falls somewhat outside the design envelope, to put it mildly.

Second is maintenance. Even bearings need inspection, occasional lubrication and replacement of worn-out parts. If that has been overlooked, it will eventually lead to failure.

Furthermore, if a bearing seal can fall off, I suspect there is something seriously wrong because such a thing should not be able to happen with normal use.

If a seal is missing, the bearings probably need to be disassembled and cleaned before lubricating them. Ball- or roller-bearings and dirt are never a good mix.

You can check the condition of a bearing by lifting the axle off the ground with a jack, grabbing the top and bottom of the wheel and try to wiggle it to and fro. There should be virtually no play. If there is play, the bearings are either done for or badly adjusted (some configurations can be adjusted) in which case they probably won't last much longer.