In reply to Baron Weasel:
You'll need to give them a wash I think.
Once you've got them clean and not smelling of death, put a few drops of clove oil in them.
When you've finished climbing, make sure you don't leave them in a bag or anything to go mouldy again. Put them somewhere they will dry well and put a sock-full of cat-litter in each to absorb the moisture.
The smell is caused by the bacteria so it's important to remember not to create an environment for it to thrive (warm and sweaty).
I've tried freezing them in a bag before but any smell just came back as soon as they defrosted.