"Bei diesem Berg würde ich nicht auf ihn zählen."
I tried "I would not count on him on this mountain," on the grounds that it made the only sense I could think of (e.g., I would not count on him as a guide on this particular mountain, lest we fall off because he doesn't know where to tie the rope.) But no.
So, is the problem in the translation to English, or in the sentence (or in my limited imagination)?
You're right. It should say something along the lines of "As far as this mountain is concerned, I wouldn't count on him".