sign it - log it
if the log is full or wet grab a piece of paper or reciept from your pocket.
if you dont have a pen or pencil dip a stick in the mud or burn the end to sign in charcoal.
ive found a way to sign every cache ive been to even if i had to dump water out of the container and make a new log book.
if i can see the cache in the middle of a river and just take a picture. that isnt a find.
logging is the reward for making the find the right way