I always start with nets on, get the pup used to rabbits in the net, let it hold them in the net, when happy, leave a couple of nets off, let it chase back to other holes, encourage the pup to fill its nose with scent at the hole. Leave the nets off for a couple of chases, then when the penny has dropped combine it all together. Marking, working the nets and chasing bolters. Patience.
I'll have some of that