I have never seen a fence that looked that bad before 
Mixing for the x-jet is about 1# Ox/1 gal h2o?
How is it with the plant life? I'll be ok with regular pre-wetting and rinsing?
1# to about a galon and a 1/4 will be fine. I have never had a problem with plants or grass, prewet the vegitation real fast and a quick rinse is all we do and its fine
That fence probably had a broken head and just was spraying on it for a while.
One other thing about ox on concrete, if the people have a well and havent fixed the rust problem, the rust at times can reappear in very little time, even if they did add rust remover to their system it still may be in the ground and run off onto the concrete and turn it rusty. Usually it will be alright for months. I make some aware that stains may reappear. I actually had a guy call one and said it was all back 2 days later. I thought YA RIGHT, this guy is up to something. I went back and yup it was all over again, not as dark but pretty bad. His lawn was loaded with iron, nothing I could do. I asked him if he wanted a monthly service.
