Its usually not a good thing when you got a Dutch Shepherd that doesnt like to bite. They always say that Dutch Sheps are slow to mature and the ones that Ive seen from a young age seem to be that way. Does the dog seem to have alot of defense? Messing around with its confidence? I would suggest keep working the prey bites and build up the mechanics of it being careful not to stimulate the dogs defense( if confidence is the problem.) When the dog gets a little older and mature you could put it all together then.At this time I wouldnt be putting anything that the dog could consider pressure while on the bite, make the bite as enjoyable of a game as possible. Once he feels absolutely good about that, and matures, if there is a typical Dutch Shep in there somewhere it should come out.

DAvid is right, sport bite training should be very enjoyable to the dog. There should be no pressure at all during this work. Take your time and go back to basics. Try what I said before and see if if works.

I have dropped back to basics (rolled up canvas tube) on a bungie type tie-out. I've been frustrating the dog and allowing him very few actual bites, also if he loses the bite then it's too bad and I start frustrating again.
As far as his lineage, his father was a KNPV I and either FR I or Brevet and his mother was a FR I or Brevet. So, I believe the background is there, it's just a matter of bringing it out to his full potential.
We work mostly in prey drive. There has been no official defense training session yet as I feel he is still too young. He has shown some civil/defensive drive on previous ocassions although not during a bite training session. He is not overly defensive though, as he will approach strangers, but is not overly eager to interact with them. Clarification: He shows no signs of fear towards them, he just doesn't care one way or the other about them (reserved?).
After reading the posts here and other e-mails I have sent to folks, I believe my concerns are more a result of his age rather than anything else.

I sounds like you are doing right. Just remember to take it slow and DONT OUT THE DOG at all right now. Grips get weaker when you encourage the out alot in early bite work.

I agree, dont Out the dog too soon, I started doing that to soon and now she mouths the item when she comes into my arm and sometimes even drops it her self !!

I found that with my Mal her grip was weak at first. This frustrated me to no end! I thought I had a weak dog, or that I was a poor handler/trainer (or whatever you want to call me) then I realized I was just being impatient. I went back to the basics and everything changed.

I used a tie back with a bungee attached and worked the dog on that line for hours at a time (with large periods of rest inbetween bites). The helper would frustrate the dog coming by to allow a bite and would then pull back to keep the dog from getting the bite. Over time the drive and desire mounted and the helper would allow the bite. Once the dog bit, the helper would put up a bit of a struggle to increase the dog's drive. Once the dog was getting into it a little more the helper began to pull away. By pulling away this caused the dog to focus even more on maintaining the bite. The bungee cord allowed movement without risk to the dog and also created an opposite force pulling on the dog. If the dog wanted it bad enough then she had to hold on and bite deeper and harder! All the time I was by the dog's side praising her and petting her to maintain a calmness about her.

After a couple of sessions working her this way the bites were completely different. My helpers described them as more full and definately harder, actually leaving some bruising through the sleeve.

Try this and you'll see a world of difference.

Take your time with this dog it sounds like the dog has a ton of prey drive and no defense which is fine he is still so young you may want to start working him on a tie out and have your helper make a lot of misses and build frustration this will help. you may also want to work the dog on a bungee to help firm the bite dont forget he still so young by the time he is 3 he will have matured and become a much more serious dog

good luck