Only time I have held back dogs (by collar) if working multiple dogs and the rabbits are flying out thick and fast.
No point in two dogs chasing one rabbit, givin others a free run..
Depending on whats going on, I have even let the rabbits get some distance, if they are breaking across a open feilds.
But if its clearance use purse nets,longnets and the dogs are off the collar
I admire keen ferreting lads its really hard work, moping up small numbers in thick cover. I am to lazy
I would make no money ferreting if its not going right, I often like to down tools and look