Hi Riverstar
I love GSD's and your's is beautiful ....
Anyhoo - like the others my Jonty (6 mth old RR and hello to Bruce06 by the way) is also on Royal Canin. He loves carrots and apples and I'm about to try the sardine thing. I'll also have to try the yoghurt trick re: farts (wonder if that would work on my OH ).
I had a couple of dramas when we first bought him home as he would often eat things off the ground and end up with an upset runny tummy, also some popular dogs treats have a horrible effect on him (he once woke the neighbour up with his howling - she thought he was dying or something).
When this happens I starve him for 24hours (just access to fresh water) and then put him on chicken and rice (as per MyCatMilo) and slowly introduce him back onto his usual.
With regards to your Lab x, Royal Canin has a Maxi Light to help with weight loss - they also do special breeds for GSD's and Labradors (sorry if I'm sounding like an ad for RC).
Good luck...
MP