Old-style (non machine washable) wax coats made for actual working country folk are waterproof but (as they always have) need rewaxing regularly, with liquified wax and elbow grease not the aerosol spray, paying particular attention to the seams.
You have to shop in the right stores and ask the right questions to get shown the ones designed for actual hard work outdoors. The Chelsea Tractor brigade like 'em thinner, machine washable, and don't need the waterproofing or rip-proofing - and will pay through the nose for the look and style without the weight and need for maintenance.
There are other waterproof jackets - Jack Murphy is a decent make but other lookeelikees can be as good and a lot cheaper - but (a) none of them IME are thornproof (which means they shred on brambles and barbed wire), and (b) most of them don't *breathe*, so if you're working in them, pretty soon you're wet inside even if the rain hasn't permeated.
Whichever brand or type you get, get one with a proper tweed lining (made of pure wool not manmade fibres), because (a) tweed is waterproof for quite a long time even if the outer is breached, (b) wool tweed will continue to keep you warm even when it does get wet, (c) wool tweed breathes so your sweat can escape and you don't get wet from the inside out, and (d), tweed is very strong, so whilst not totally rip-proof, it will repel brambles and to a degree barbed wire even if the outer gets ripped.
Check the lining of the sleeves too, they often put a nylon lining in there, so your arms get wet - my pet hate.
If you're not a fan of all that effort and maintenance, try angling shops. They will have 100% waterproof coats, and will have some which are heavy enough to withstand brambles. They probably won't have tweed linings though, so if you'll be working hard, you will get wet from the inside.