I work proofing as I am building the behavior. At each stage of training a running, once they are looking solid at it we work around the clock with a jump coming off the contact, turns to tunnels, turns away, distances, fronts, rears, blinds, pushes, and me being ahead and behind. By the time I have a finished running with 95% accuracy I have a dog who I can do anything with and expect the same performance.
We had a hard push off the dw last weekend with no other way to get it done with a running and both girls still nailed their contacts. To me, that tells me they are pretty solid. A push with a running would drive a less solid dog off the contact.
Essentially I work for run fast through the whole contact down through the end regardless of what I am doing.