If you mastiff has a fear of loud noises, gun shots, fireworks, thunderstorms, and other loud noises, is a very common among dogs. If he or she is displaying signals, like shaking, trembling, hiding, trying to run away, barking, urinating or uncontrollable pooping, these could be some of the signs.
You can sometimes treat this with behavior modifications, general change of environment, and even prescription medicines.
One of the best ways to make the dog better, is to change his or her own living environment around. You should increase the dogs daily exercise program, to make it physically more drained.
Give your pet his or her own space. Pets love to feel secure and protected. Try to make the a crate or sleeping area, that give them comfort, and has some walls up around them, so they do not feel like that have to worry about things coming at them, from all directions. Dogs usually like to find nice places to relax and sleep, like under chairs, tables, places where they feel safe, they can sleep, and still keep one eye open, to make sure they stay out of arms way.
Give your Mastiff a more noise friendly atmosphere. You could turn on a radio, or run a fan or other mechanical noise maker that is peace full and continuous. This is good if the dog can hear noise outside, like kids yelling and playing, other dogs barking, construction going on, it helps tone down the noise, with other continuous noise, to calm the dog.
Do not overly give your dog extra added attention, like petting him or her longer, they might interrupt that as a good reward for acting bad, just treat your dog normally.
One fun way to try and teach your dog not to be afraid, is to give him or her their favorite treat or snack, each time the load noise is going to come. If it is a thunderstorm, each time the loud bang comes, give your dog a treat, they will look forward to more thunderstorms!
If you want to train your dog not to be afraid, you can obtain CD's or downloads from the internet, of thunderstorms, fireworks, gun shots, etc …. and begin by letting your dog listen to these sounds, at low volume. You will gradually increase the volume over time, and give your dog a treat when she does not freak out to the sound, and slowly increase the volume each training session, then slowly do less and less training, until your mastiff does not have any more fear of the loud noises.
If this does not suit you, there are medicines available from your veterinarian, that you can give to your dog, before a storm or load noises, to calm him or her, the old fashioned way, with prescription drugs.
You should be able to find noises on line very easily, with all the major search engines, just type in thunderstorm sounds, and you will be on your way!