Oh noes, my sleeping mat!

So, we've just moved into our new house, and since we don't have any furniture, I slept on my self-inflating mat. I have 2, a Therm-a-rest (Prolite) and a Denali (from Anaconda in Brissy). I "slept" on the cheapo Denali.. and well it turns out there is a hole in it. I learnt this because I didn't sleep at all, and I was incredibly cold. Anyway, my question is this: If anyone else has any experience with a punctured SI mat, what did you do?
I have searched (audibly) for the hole, but no luck. I'm pretty sure it's not the valve, since it doesn't seem to leak when I sit on the mat, but there is definitely a leak somewhere! I found a topic where a member mentioned that the polyurethane coating can degrade and allow mass exodus of air (http://bushwalk.com/forum/viewtopic.php?f=15&t=5462), but I don't know if that is the case here.
What does everyone recommend for finding the hole? Immersing the mat in water (would it ever dry??)?
Many thanks, as you will be helping me get a good night's sleep!
Cheers
Dave
I have searched (audibly) for the hole, but no luck. I'm pretty sure it's not the valve, since it doesn't seem to leak when I sit on the mat, but there is definitely a leak somewhere! I found a topic where a member mentioned that the polyurethane coating can degrade and allow mass exodus of air (http://bushwalk.com/forum/viewtopic.php?f=15&t=5462), but I don't know if that is the case here.
What does everyone recommend for finding the hole? Immersing the mat in water (would it ever dry??)?
Many thanks, as you will be helping me get a good night's sleep!
Cheers
Dave