the livestock are going to rub them, kick them, bite them, ram them, scratch on them, and just plain down running and go attempt through them.
my issue with longer single gates, is that they get stuck in the mud eventually, and/or frozen into the ground or with snow piled up on them.
preference is to use a "wheeled jack" you might find on a trailer / boat trailer. pick them up fairly cheap (got 2 that were like 15 bucks each on sale at menards a few years back). quick and easy twist of the jack handle to raise one end of the gate up if need be, and then wheeled assist. so your not having to lift it up as you walk it back to were it needs to go. just place the wheeled jack clear out on the end. i just used a couple 1x6s boards so i had something to wire to / screw when attaching to the gates.
those long gates even the lightest weight you can find. the fence post that it is connected to (hinged post) even with extra bracing to next post in the fence. is still going to want to move some. causing the gate to drop down into the ground. it may be good for a couple years but after that.... reason i prefer the wheeled jack approach, only a few bucks, and makes gate easier to deal with in the "ugly times" and more so when ya got a few piles of manure heaped up by gate ya need to get over (jack the trailer up err gate up).
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when gates is closed = want a nice parallel to the ground and a couple of inches of ground if that. to keep the dumb dumbs from putting there head under gate and lifting the gate up off the ground and running through the gate. grass is always greener on the other side!
how gate open doesn't really matter. as long as it opens without having to lift it up and drag/pull it across dirt up a hill. other words gate needs to swing freely other than that. it doesn't really matter. some wire / bungie / dog leach / cat leash / etc... can be used to hold the gate open and/or closed. personally though i prefer gates to swing open if not latched in place. though with live stock at times is nice if gates swung shut.