Elka's favorite game is Tug. She will try to play it with any toy ever, from a rope (you know, marketed as a tug toy) to Gumby (who puts up with it), to a tennis ball (which fits almost entirely into her mouth and doesn't work).
Tug is a fun thing for her, and can be for me too, though the game has to have rules, as one might guess. There are some people who in fact say that you should never play with your dog, as it can mess up the "pack hierarchy" or make your dog aggressive. I don't
really buy into the whole "pack" notion; dogs know the difference between people and dogs. A whole bunch of dogs together might make up a pack and have rules within it as such, but if you've got people and an "only dog" in a household, I don't think it applies.
Aggressiveness is a can of worms I don't really want to get into, or at least not when we're talking about a fun game! Suffice to say, if your dog has aggressive tendencies in the first place, or is very very possessive with toys, don't play tug. There are problems already in place and you don't need to ask for more. But if you have a well-balanced dog who lets you give and take toys happily? Tug away!