Was it a mistake to put in an underground fence?

I'm asking this because I took my 7 month old Eng Springer Spaniel out to a field to do some work for the first time in a while (first time since I put it in) and now he just runs back to the truck. Even when I carry him out to the middle.

He's fine in our yard and my girlfriends yard but not the field?...

any advice?