Where do all the old nets go?

It is encouraging to see the global efforts at scaling up malaria control interventions especially the use of long lasting insecticide treated bednets (LLINs). I was involved in one of such campaigns to distribute these nets as part of an evaluation study.
In the course of these visits, I was struck by the many "uses" that bednets are put in these villages. The question that struck me was that we did not have a way of monitoring when these nets expire and the next big question was "what do we do with the expired nets"?
At the moment I haven't got a clue and most literature seems mum on the subject. I would be glad if I could get some insights to any methods for monitoring expiration at field level recycling of LLINs.