My 7month old retriever has suddenly started messing in the house. On most occassions (like this morning) he has already been let out for the toilet, come back in, waited until my back is turned and then done his business!!  It has usually been in a different place each time.  I cant think of anything that might have upset him - in all other ways he is a really well behaved boy.
The only thing I can think of is that he went into kennels a month ago, just for 5 nights but in the following week he messed 2 or 3 times.  He has a crate which he likes and he goes in there quite happily if I am out of the house and at night.  I dont want to have to put him in everytime I go upstairs!! 
Do I go back to basics and treat/praise him everytime he goes outside?
Any advice much appreciated.

He's at an awkward stage - he's a 'teenager' and that on it's own often brings about a slip in house training habits, but he's also been stressed by his stay in kennels (where he may also have unlearnt some house training) AND if you are in the UK (unless you are very lucky) you'll probably have been experiencing fireworks - which may also upset him :(

I'd go back to basics, so he re learns the garden is the place to go.  Also make sure you are cleaning up properly in the house (using bio washing powder followed by a spray of white or surgical spirit when the surface is dry)

Your Lab is still a baby,like Digger says he may of been stressed at being in kennels and maybe got confused with his toileting,just start house training again I am sure it wont take long,my Annie was only fully house at seven months,when she was about ten months she was playing up ,running around at 60 mph suddenly did a big wee on the rug, never done it since,she was just excited.Good Luck.

Sheila.

I'm definitley not an expert but have you had him checked out with Vet?  Maybe he picked something up at the Kennels?  I've just had a similiar problem with my spaniel where she was fine and didn't mess in house to suddenly starting to mess...turns out she has a UTI and is now on anti-biotics for it.  Within a day of visit to vet where she got a shot, she was improved.