when taking your dog out ferreting, a couple of hours once a week is plenty, i done this with my pup when she was 5 1/2 mths old just to let her grab a few rabbits in the net, then gradually up her ferreting outings to 2 days a week for 2-3hrs, this has worked for me so far, she is now 10mths old and for the last month she has started marking the warrens, i have also had her out lamping with a more experienced dog since she was 8 mths old, just giving her 1 run on a squatter at the end of the night, iam now giving her 3-4 runs once or twice a week and she is doing well so far, cheers.....