Josh is spot on with proper fencing. One thing I would say is the first advice I ever got in deer farming was to wrap the brace wires so that bucks could not get tangled in those wires.
Driving posts with a post driver will make a significant difference and allow you to shorten the spacing up without sacrificing integrity. Driving steel post is even better because you can just go till you get solid ground... I've got a few 24 ft posts driven 16 ft into the ground with an excavator, and several 10' T posts driven 7ft into the ground to anchor low spots on my perimeter fence.
My braces are now all 5" steel posts with 2 horizontals at 6 and 7 ft. Ideally with 2 one would have been lower but I wanted them high so that it was one less thing to potentially hang an antler. Then I have a third post with a welded angle brace from 6 ft to the ground.
On my dividing pens I have put 3 horizontals, bottom, @ 4 ft and @ 7 ft because i framed 4 ft guillotine gates in them. Since my pens are on hills all my future corners will have a brace along the bottom as well to hang belting from if the wash out.