No problem going across with a gentle "U" shape topline . it looks like the fence to the left is needing some repair or replacement. Is that your fence or a common fence? You sure don't want to tie into that with this fence. Two choices..first if the new fence is "T"ing into old one, rebuild old fenceline with same type as new fence going both directions maybe for 10-20' for now or replace entire old fence at same time. BTW, on the other end (I can't see),you will need some kind of "L" or "T" brace as it won't be sturdy enough to just kill fence on a straight run.Please consider pipe instead of wood..reason is zero maintenance..no rotting posts in very wet area..du
Top photo is 2 7/8" posts with 2 3/8" top rail & 48" 2x4" wire, the BLURRY bottom photo shows double H braces, T posts & 48" wire. In this situation the T posts are driven to 4 1/2' deep, not set level across top as described for wood posts..
