waterproof socks are a must i presume?
I've seen a few people recommend them recently, but it's not something i've considered as in my head if any water gets in then it's trapped in the sock and can't drain out. I imagine it'd be more important to have a few changes of socks.
Although it's why i'd prefer to look for something in Spain in the cooler winter months. Still generally dry but not too hot. It's a shame some of the more well known races are so bloody hard to get into, especially for people like me that're slow.
I have Sealskinz for MTB and they have these weirs rubbery cuff seals that (a) stop them from falling down and (b) stop water getting in. Not sure how they would be during a run, but maybe there is a thinner version for that kind of thing.
Their are loads of races and i think the smaller ones are best in general. They can be hard to find, often no English and no attempt at SEO so you almost need to be told about these races.