Don't have a picture for you, but not sure if you really need to do all that undercoating.
I had a three year old FFE in Chicago. Driven through Chicago winters and summers for three solid years. Before returning the car for one reason or another, I removed the headlight assembly on the car. I was kind of surprised to see rust, it was really just surface rust, at the frame to bumper joint. The three year old California car sitting next to it, with the headlights removed, had absolutely no rust in the same place.
My point - if you are trying to really rustproof the car, you would never get up in that area under the headlights. And there are far too many hidden places for rust to happen. Not sure if just spraying the bottom of the car will do you a lot of good. The rust will appear in other places in the car - if it does. And it will likely take a really long time for rust to happen.
I'm also not sure Focus MKIII's have any real rust prone areas. That version is about 6 years old now, and I don't see any Focus that have rust anywhere. From personal experience, it is nothing like the Mercedes around 1999 - total rust buckets.