Wait until the hides go under something. The “active” part will likely emerge when the target becomes inaccessible. Right now, there is no need for Salu to be active because the target is right there.
Be very aware of what this looks like for future reference. OFTEN, after dogs develop an active segment to their alert behavior chain, they don’t know how to indicate on a surface truffle. For advanced truffle dog teams, surface truffles become incredibly challenging because there is nothing for the dog to “do” at the truffle site.
Encourage some precision at this point, but don’t worry about the active alert until there is a barrier between Salu and the truffle. That will be a nose target or paw (we recommend nose). At this stage, continue marking and rewarding as you have been but add a request for a targeting behavior when you go to pick up the target. This means you will be giving two rewards…one for finding the correct hide (as you are doing) + another reward for the nose/ paw target. Then leave the scenario with the truffle target in hand.