In reply to zebedoo: If you're making extendable quickdraws then I wouldn't use retainers at all. One of the beauties of these type of QDs is that you can clip the gear then unclip the rope end krab and clip it back in to any one of the free loops and the thing will extend. You can't do that if you have a retainer on the rope end krab. It's still worthwhile being able to tell which krab is the rope end and which is the gear end, but I do that by krab colour. I know this is contrary to the advice given on Planetfear, but it works for me. Your experience may turn out otherwise.
I wouldn't carry a whole rack of extendable QDs due to the bulk of the tripled slings. I normally carry just a couple of extendable ones in addition to a mixture of 15cm and 20cm fixed-length QDs. I do use retainers (girth-hitched o-rings) on the rope krabs of the fixed-length QDs.
As far as any dangers of using retainers, I'd be very surprised if a stretchy rubber retainer that you could fit using only finger strength could damage a sling. Remember slings aren't designed to be dynamic, so there's no special elastic qualities of the material that need to be protected, unlike with a rope. Petzl actually market the String as
protecting the sling from abrasion:
http://en.petzl.com/petzl/SportProduits?Produit=345 I'd suggest that there is a counter-argument that it
could trap grit would would
cause abrasion - but the weight of logic and evidence on either side of the argument is probably so small that it makes no odds. Best practice is to check your slings & QDs regularly for wear and abrasion anyway.
The one thing that Petzl do say is risky is clipping the krab the wrong way through the retainer, as shown if you click on the "Sling + STRING: possible danger" link on the Petzl page I referenced above. Anyone who put their QDs together that way would be a prime Darwin award candidate anyway, IMHO.
