
I've had borzois for over 20 years, was hoping for a saluki and am picking up a Silken Windhound pup tomorrow and I live in the country and don't own my own field :-) Are you north or south of the border? Here in Scotland we have the right to roam, which means you can use any empty grass field for exercising the dogs. In England you may have to ask permission.
I have several regular fields I use depending on livestock rotations. They range between 2 and 15 minutes drive away. Go round your local area just now and make a list of suitable fields. You need to walk right round the perimeter of the field checking the fence, ideally it should have no hidden dips and it needs a gate that closes. The ones I use are all bordered by roads or railways lines rather than other livestock fields. Only once has one of my dogs ever jumped out of a field, after a deer but that's the chance you take when you let a hound off lead. I've had thousands of trouble free walks and hundreds of times when they've got up after a rabbit, hare, fox or deer but stopped at the fence.
Regardless of how much free running your hound gets your garden still needs to be secure. Salukis are a lot like zois, after an initial race around they'll just mooch along at your side unless they see something to chase. Even after a long walk they'll still want to chase the sheep in the next field if they run. Hedges make good boundaries because they can't see through them, sighthounds have no wish to chase anything they can't see. What height is your hedge and is it solid or with gaps? A 4' chicken wire fence on your side of the hedge would be fine. I've got 6 foot fencing in the back garden but only 4 foot in the front. Generations of borzois, a whippet and a lurcher plus several collies have lived here and never shown any inclination to jump out even after such delicacies as a passing cat.
You'll learn that walking a sighthound is not like walking any other breed. Paths with lots of undergrowth or trees are not ideal as they could very quickly disappear from sight after prey. I try to stick to large open fields to walk hounds and just keep scanning the horizon for anything they may find tempting :-)
As with any other breed let your pup off lead as soon as possible, but don't relax and think your hound is perfectly trained and not like all the others, sometimes the chase instinct doesn't kick in till a year or even later.