Yep, i'll agree with that, if you regularly wade to those depths then you should be checking your bearings pretty often..
If you get to them before they're knackered you can clean them, re-pack with grease and replace the seal, you'll do them all in a day, and the seals are not expensive.
Use good grease, I use JCB blue lithium grease, its waterproof and really sticky, its improved the life of my wheel bearings quite a bit...