It helps to understand a bit about the KNPV program. I don't claim to be an expert in the Dutch system but have experience with quite a few dogs from their clubs. Very early on guard behavior is promoted on the box and other inanimate objects. Often this involves some compulsion/conflict. When subjected to new experiences they often revert to the previously rewarded behaviors of barking/guarding. Since this is a big part of the KNPV then they have had a great emphasis on these behaviors. So it is easy to see where the problems come from when doing the work in detection.

I am big on developing the actions of making prey for the objects and making the objects smell like our training goals for the INITIAL work. this is often coined "primary reward system". In this work the goal is to snatch the toy...in the dogs mind the critter from its hiding spot first and if that doesn't work then to flush it out (analogous to a bird dog "setting", "pointing" or a terrier "going to ground" or digging) to get the prey to action.

So I go to a lot of work with a dog chasing the "critter" into its hiding locating and allowing drive satisfaction behaviors approximating the goal we would like to see at the end. It may start with the dog simply rooting at the location the "critter" disappeared to, then on to the scratching behavior. Allowing the flushing of the critter to occur at just the moment you choose as the next step and withholding if you don't like what you see. The critter can only respond to the correct actions (keeping in mind the concept of approximation) once it has disappeared and cannot come out for any other reason.

Some things often help with this process: that when flushed the critter fights for its life..using a line tied to it it tries to escape back down the hole it was flushed from and once it escapes from the dog it always disappears back into the search areas or even back into the hiding spot. Changing the type of critter....rubber hoses, dowels, rolled cotton towels, etc. are useful. They should change a lot and always be clean of dog slobber.

OK the above is ONE way.

Another is to abandon the classic approach to drive development and use a conditioned reinforcer (a word or a clicker) to gain an edge in timing. This means of doing detection work is dramatically different that what you probably have been using based on your description of the equipment you are using. So, I will simply say that in your situation, I would not g this route unless all other means are exhausted. It means a big paradigm shift for most trainers.

Lemuel I completely agree with David and Matthew. It sounds like your dog does not understand what he is being asked to do, so it's time to go back to the very basics of detection training.

Since your dog is aggressive alert I would start with the scratch box that has plexiglass. Tie a piece of string or rope around your reward and run the string / rope through your scratch box and out the back of the box. Place the reward about 10-15 ft in front of scratch box and have a helper holding the other end of the rope behind the scratch box. Put the leash on your dogs flat collar (you don't want it to be a correction) then have your helper start pulling the reward into the scratch box.

As your helper is pulling the reward towards the box, give your dog his command to find dope and allow the dog to go towards the reward. Keep back pressure on your leash so your dog so is not allowed to run and he is having to pull you (like your compressing a spring). Once your dog is about a foot or two in front of the box, have your helper close the front part of the box and give your dog some slack in the leash. As your dog begins to scratch on the box, give him tons of praise and be very high & happy in your voice. After a good two paw scratch give the dog his reward and play lots of tug. The praise ratio should be atleast 5:1.

If you do this drill several times a day and you use your find dope command, the dog will understand the game and not confuse it with object guard.

In the beginning stages, I would not use multiple boxes or objects for detection training so it does not confuse the dog. I wouldn't use your type of scratch wall in the beginning stages either. You can build a similiar wall that has holes cut it in and a piece of curved PVC coming out of the back. When the dog alerts and indicates on the approprite hole where the odor is hidden, have your helper throw the reward down the PVC pipe and it will reward the dog and the source of the odor. Good luck