(need answers to these very quick )
1.what are some common causes of exercise-related injuries?
2.how can mental alertness to prevent injuries?
3.how can training specifically for a sport to prevent injury?

over-exertion, pulled muscles, dislocations, and sprains.

Cross-train. Vary your workout. Don't overuse one set of muscles. Repeating the same muscle movements frequently can lead to overuse and repetitive-use injuries such as shin splints and tendinitis.

From what I understand mental alertness helps you decide from what's dumb and what you should be doing like for example if someone went to go walk across the street it's your mental alertness that helps you see if it's safe or not... your mental alertness can transfer signals to your body why helps you stop doing it physically so if a car was coming and you were in the middle of the walking your brain censors the danger that is approaching to have you run across or to not cross at all; where as the driver mental alertness sees the danger on what's happening so that's put into physical alertness to stop the car but truly i dont know it's worth a shot

Follow these tips to keep yourself injury free: 1) Stretch: Having good flexibility decreases your risk of injury, so incorporate stretching into your training regimen. ... 2) Always include a warm up: Muscles respond to heat and will have a greater tolerance to stretching when warm.

i think he will be okay, id probably take the dog to the vet just incase