My dog is having sudden issues coughing. Please help!?

He is a mini Australian shepherd, and he has always been at least a little warm here (Arizona) due to the extreme heat (he has a lot of fur). So he pants a lot, but other than that he has always been fine. Yesterday, my mom asked me to lock him outback. So I did (in the shade and with water). He is a very high-energy dog and did not take kindly to this. He ended up knocking a trash can over that was full of old cigarette butts from my parents. I think it is likely that he could have eaten cigarettes, or at least inhaled a lot of ash. Now he is coughing and gagging at random intervals (but still seems mostly fine and happy). Like I said, this is all very sudden. He is still just a puppy, though he is almost two. But his whole life he has ran around the yard and done so, so fast we can't catch him when we're playing and never had coughing issues. He is really loved by our family, and I would appreciate any help or advice you could offer.