A good teak deck should almost never be sanded. To care for them, wash them is soap spuds from ivory soap or the like. And that is it. If they get really dirty, use a semi-stiff plastic brush on them. Always brush across the grain, never with it.
Eventually the caulking between the boards will need replacing. dig out the old caulking with a small screwdriver or the like. Make sure you get it all out. The cover all the teak with a layer of masking tape. lay your new caulking compound in and use a spreader to ensure it is all the way down. Peel away the masking tape
Voila! watertight teakdeck.
is much easier............