Gel knee pads from Harbor Freight...one of the best tools for MD that I've found. I had a partial knee replacement last December and have been given the "all clear" to be able to dig again. Lots of folks have mentioned sand hunting...one of the worst things you can do with bad knees. Sand is unstable and causes your knees to "shift" to stay in alignment, causing pain and possibly more damage to the knees. I would have thought because sand is "soft" it would be easier on the knees...No say the orthopedists. I did try to hunt the sand this past summer and the docs were right. Ouch!
You mentioned that you were watching your carbs at night. Unfortunately, this will not help you lose weight. If you are watching carb intake, you need to do it all day long to get the best metabolic effect. You need a certain amount of "good" carbs. Low carbs help to burn body fat. The Atkins diet (the original one from years ago) was a great fast diet. You cut your carbs to under 30 grams per day for the first 2 weeks. Then gradually you added more carbs. You continued on this reduced carb diet until you reached the point that you were at the weight you desired. This becomes your "maintenance" plan. Add more carbs - you gain weight. Deduct carbs, you will start to loose weight again. Also, watch out for "hidden" carbs - fruits and veggies (carrots, yams, beans, etc). For the first 2 weeks, you cannot have any fruit, some limited veggies. Lots of lean meats, some dairy, some green salad veggies, and lots of water. Some people say that Atkins is a horrible diet (have beef with a side of beef and butter is an often voiced comment), but my husband and I have been on and off Atkins for years. When on, we feel terrific and are thinner with lower blood pressure. When off it, our cholesterol goes up, blood pressure goes up and in general we feel lousy.
I am not a doctor nor nutritionist - I just play one of TV.

The above is just my humble opinion. Of course, before starting any diet or exercise program check with your health care provider.
Good luck with the knees and the dieting! I feel your pain on both.
Anita