Elka loves toys that we can stuff food in. Even if it's just a schmear of peanut butter, she'll spend (what I feel) is a disproportionate amount of time rolling it around, holding it down with her paws, dropping it, and licking it.
This kind of "work for your food" activity, no matter how short, is good mental stimulation. The Kong rolls around, has knurls inside that trap the food, and doesn't really have a big enough opening to entirely accomodate the DoberTongue. Frequently, mental stimulation can be more tiring than physical exercise; perhaps it just puts dogs in a mental mindset, so that they recognize fatigue? That's my best shot at speculation.
I can't claim to be the canniest of Kong users, but I do have a few tips for making a Kong last longer than five minutes.
Your "foundation layer" is where you start; this is what goes in the very bottom of the Kong, by the little bitty hole, in the narrow part. It's nice to put something of a bonus treat in here, that your dog can smell, but obviously can't get to right away and has to work for. A piece of pepperoni, a single ravioli or tortellini, or a cube of a cheese like cheddar are all viable options. I sometimes stick one of Elka's vitamins in the bottom; they smell like bouillon and she seems to like them well enough, so it works.
On top of your "foundation", if this is a food Kong instead of a treat Kong for fun, you'll want to add your dog's kibble. If you feed both kibble and canned, you can mix them together, stuff the Kong to its brim, plug the opening with peanut butter, and freeze it for a bit. Freezing adds to the time it takes to unstuff the Kong, the cold Kong will also feel good on teething gums, if your dog is young enough. If you don't use canned food, then you can stuff as follows: Foundation layer, kibble, peanut butter, kibble, baby carrots (cross them in the Kong so they're a barrier), peanut butter. Layers add to difficulty, as do foods of different shapes and sizes.
Another Kong stuffing "recipe" that Elka has enjoyed is from the Kong Company website itself (it pays to go to the source!). The basic gist is you take a medium sized banana, a couple tablespoons of wheat germ (unless you're grain free!) and some plain yogurt; mash these things together, stuff into the Kong, freeze. In this instance, you could put a slice of intact banana at the small end of the Kong. It would certainly help prevent leakage as the frozen treat melts! Peanut butter is another good addition to this.
Really, I pretty liberally peanut butter my dog, though if you're allergic to peanut butter (or your dog is) you can use spray cheese or something else that's somewhat sticky and viscous. I can suggest Tahini, which is remarkably like peanut butter, but is also remarkably expensive. But, if you've got a jar because you bought it to make hummus or satay and haven't used it since, then by all means apply it to your dog before it goes rancid.
Kong toys are reasonably chew-proof and come in a variety of shapes, sizes, and formulas. The Kong Classic is the one best suited for feeding your dog out of (I feel), and Elka's first Kong was the puppy formula, which is a light blue marble-y color. The Kong Flyer is a good and durable frisbee, the Kong Bone makes for interesting chewing as well, and they even have squeaky Kongs, if you're into that. And, if your dog is a beast whose jaws know only destruction, they have the Extreme Kong line, which is made out of a slightly different formula and is black, and is apparently even sturdier than the regular stuff.