When out in the park with a pup, it can be necessary to improvise on pet toys. Thankfully, most dogs who like to fetch will happily fetch most anything... especially sticks. Search for a stick with a width and length that's both small enough for your pooch to easily handle, but also big enough that the entire stick can't fit into his mouth.
On one visit to NYC's Tompkins Square Park, I watched a beagle happily fetching sticks (in this case, more like twigs) when, all of a sudden, the pup didn't come back and began alternately running in circles, rubbing his head on the ground, and pawing his face. The owner rushed over to the dog and, thankfully, realized what was wrong. He stuck a hand into his pet's mouth (while pushing lips over the teeth to prevent accidental biting), swept his middle fingers across the top of the dog's mouth and brought them out with a stick. While I am not advocating sticking your hands into any pet's mouth – especially a frantic one – please be careful when playing fetch with small objects that could get lodged, or splinter to get lodged, in his mouth or throat – you don't want to panic with an equally panicking pooch!