I have a 10-month old male Yellow Lab, named Ernie.
He is about 100 pounds now, and I don't expect him to get any bigger. As far as training went...potty training was a breeze. And most of the basic commands and house rules he picked up on very quickly.
And he is a very friendly dog. As far as protective however, all I can say is that I am lucky that he has a loud bark. LOl....
I do not kennel him, and he is very good in the house. He does not come on the carpet, or sit on furniture. And he is not a begger...which is my biggest pet peeve with dogs. He loves his outside time and is a very good running partner with a lot of endurance. However, remember that labs are hunting dogs, and swimmers...so he can become distracted easily by wildlife.
I had him "fixed" at 6 months, and even though he was good before....he became more calm indoors and it made him less apt to stray from his yard.
The only thing I would have done differently, is knowing that he is indoors often, I should of had his tail docked. You would probably have this done anyway though since it is a Rott mix.
Good Luck & have Fun!!
~toga