"My dog finished the activity in less than 2 minutes! How do I make it more difficult?"
I hear questions like this a lot. And I understand where it's coming from: you've just spent some time coming up with and preparing an enrichment activity or toy, and you're expecting your dog to be occupied with it for a while so you can eat your dinner or get some work done in peace. It is a really great idea to use enrichment as a management strategy (something that promotes positive behaviors while you're not able to actively train your dog).
But keeping your dog occupied for a long amount of time should not be the primary goal of your enrichment strategies. If it is your primary goal, you are missing out on the whole point of enrichment, which is to provide your dog with a fulfilling outlet for their natural behavioral drives. You're also risking your dog becoming frustrated or bored with the activity, which can also lower their self confidence and make it difficult to engage them in future activities.
That's why it's important to consider what your dog's individual drives and needs are, and then provide them with ways to meet those needs at a level for which they are prepared. You should also be available to help guide your dog through a new activity if they show signs of frustration or lack of interest.
Once they've shown that they understand how to engage with a particular toy or activity (and they enjoy doing so), then you might choose to gradually increase the level of challenge. But it's important to do so with the goal of keeping your dog interested and engaged so that they can get the most out of the activity -- and not with the goal of "stumping" them.