Playing with sticks and stones might not break your dog's bones... but it CAN really hurt them.
As a professional dog trainer, I've been lucky enough to work for, with, & befriend some really wonderful people in veterinary medicine. While dogs are pretty notorious for getting into mischief, the stories I hear most from vets are ER injuries caused during well-meaning games of fetch.
Fetch can be a superfun activity that helps pups and humans bond (and it's also great for burning off excess puppy energy!) but please nevereverEVER use sticks... In fact, according to many vets (including my previous Pet First Aid instructor), stick-related injuries are THE NUMBER ONE ER injury at many vet hospitals. There are numerous causes for worry. Dogs sometimes swallow large chunks that get stuck in the esophagus or intestines, can get splinters inside their mouths, and (most sadly, and most frequently) there are countless stories of dogs who impale themselves while catching, running, or chewing. It might sound like stick impalement would be a fluke accident... but it happens much more often than people outside the industry realize. And it's not something anyone wants to witness.
Rock injuries are another story I hear about a lot (from both my vet friends, and my dog training clients.) Some dogs (lots of larger breeds) seem drawn to playing with rocks and stones (especially river rocks & lava rocks.) Some dogs like to carry rocks here & there, toss them about in the air... some even like to chomp on them (or eat them!) While this might seem like simply odd, harmless fun, when it comes to rocks & stones... it's actually quite dangerous. Besides causing serious and painful dental injuries like broken teeth (and believe me, you DO NOT want to find out first hand just how much it costs to get dog dental work done...), rocks & stones can also be swallowed (sometimes accidentally), leading to choking and intestinal blockage.
When working with dogs who've taken a liking to sticks and stones, I've found these tips most helpful:
1) Simple Solution: Remove all loose rock/stone from your landscaping.
2) Required Action: Be a responsible pet parent by providing close supervision when in rocky/ branchy areas.
3) Easy, Fun Training Technique: Trade up. Have a delicious treat, or irresistible toy on hand when venturing into known rocky/branchy areas. If your dog picks something up, you can make an exchange. Present the treat or toy at nose level, kindly say "drop it," and when your dog drops the rock/stick, say "take it," make the switch, and praise.
This is called incompatible behavior... your dog can't open her mouth to take a treat or toy if her mouth is closed around something else. Incompatible behavior techniques work for almost anything (for instance, if your dog is in a sit-stay, he can't jump up on guests... it's all about giving your dog an alternative task that he can succeed at!)
4) Preventative Training: The "leave it" command. Teach your dog this command, and when on walks, put it into action with said rocks, sticks (and other yucky things like poop, gutter junk, etc.) Most basic and puppy group classes will cover this command, and while it can be tricky for inquisitive puppies to master, once they've got it down it really comes in handy!
5) Provide Sensory Stimulation: Be sure your dog has a good supply of supersturdy chew toys. Look for toys that best resemble the shapes and textures that your dog seems drawn to.
If your dog mostly has issues while on walks, an easy (and fun!) solution is to vary your walking route... new smells, sounds, and sights get your dog motivated to keep exploring what could be around the corner rather than fixate on those same, old, irresistibly naughty familiar locations.
Things that usually don't work with rock and stick issues:
Drama: yelling, chasing, forcing items out of the mouth. Sometimes dogs will think this feels like a game (grumpy mom tag! woohoo!)
Bitter Apple (and friends): while icky-tasting sprays might work on household items, who has the time or money to spray all the rocks in the entire yard (or neighborhood!)
When it comes to sticks and stones, "just say no"... or, more exactly... "just say leave it!" :)