I use the digital kitchen scales to weight the GP's, I just pop an ice cream tub on the top and put a piggie in - they do always have that "am I going in a recipe?" look!
The rabbits I don't weigh often but when I have had to I use the bathroom scales and pop them on in their carriers, subtracting the weight of the carrier of course.
I sympathise with your fox problem - I have extra wire panels from a run all around my aviary and hutches, I shut everyone in and I cover everyone up at night so they can't see anything nasty.
The fox pops by around dust usually, the outside light goes on and one of runs out shouting and grrrrring at him - he goes but he's not that bothered!
My neighbours dislike the fox and have added fortifications to their garden, trellis panels and spiky strips, to no avail. The only thing that seemed to deter him for a little while was me chasing him out of the garden in the middle of the night in my nightie, weilding a swingball bat! Funny, we didn't see the neighbours for a while either :lol:
I would never be confident that I had deterred him in any way, I would just make getting in to the hutches as difficult as possible, remembering that they are very strong and tend to push the wire in rather than opening doors, and make sure the buns have somewhere they can hide away should a fox come round to look at them when you are not there to protect them.