If your grey decides to chase something & happens to be off leash there is no way in hell you will be able to call it off.
That applies equally also to most other dogs except those which are exceptionally well trained & suited to training such as collies, G Shepherds etc.
Recently my girl saw some feral deer on my sisters farm & she'd gone: through the electric fence, the brambles, the undergrowth, & barbed wire.
Very worrying - but it was a risk we had accepted.
Eventually she found her way back - covered in minor skin tears & scratches. Antibiotic ointment for a week or so, & careful wound inspection, & all's well.
Greys are quite sure footed, but if brought down by irregular ground or rabbit holes, it will be tears all round.
You just have to decide, we let her run with the farm dogs, she likes to be "just a bit faster" but overall nowhere near flat out racing speeds.
At the local off leash beach, she shows off doing doughnuts at impossibly high speed & very tight turns. She can sidestep at speed any other dog we have ever seen, it's a pure joy to watch (& just about everyone does watch). Yes I guess it's a bit risky but dogs have to be dogs imho.