airedale x staghound is my thoughts, no dog will catch what your sugesting before they hit cover so you want somthing that will tear through the bushes and not get messed up soo it will need to be hairy and with a think coat and full of balls so it will lug on the back legs before turning it around, so it will have the drive to follow for awhile as well as the endurance not to much airedale but.
throw a pic of your current dog on