Im no dog trainer but alot of it stems from frustration by sounds of it. Id say burn some steam off him either a night on numbers of rabbits or maybe try and retrieve couple hares when the grounds right. All the praise in the world is not gonna matter one bit to a super keen dog thats watched other dpgs run but the only thing stopping him is you lol.
I like my dog to use his nose at night whether its rabbits in abit of long or finding other stuff without me hardly putting me lamp on but its gotta be under control. Dc you say youve never used a slip will your bitch not run if anot