How to deal with 'snappy' separation anxiety???

Hi all, My GSD (Mason) is 1year and 9months and has just started biting my dad. This is how it began....
A few weeks ago, my dad went up north for the weekend which left my mum, myself, my sis and the dogs at home, Mason didn't appear to be bothered about this until last week.
Now, every time my dad gets ready to go to work, Mason growls and then bites him. At first we thought it was 'pack aggression' but last night i held Mason's collar as dad was leaving and his growl turned into fearful, helpless barking (the kind you hear from pups when they're left alone for the first time) so i now think it may be separation anxiety. Any ideas why its only started now, why he only does it with dad and how can we help him? suggestions and ideas would be VERY much appreciated, thanks
Lisa XX

It does sound like sep. anxiety and it can manifest in this kind of distress where the dog is basically trying to stop the person from going.

I'd suggest getting a good trainer/behaviourist in in this instance, see www.apdt.co.uk or www.apbc.org.uk