Instead of using store-bought, commercially-made flypaper, make your own using ingredients that aren’t poisonous.  Use any type of paper cut into 2” strips of any length.  Punch a hole in one end of the strip to put string through for hanging.  Combine ½ cup of corn syrup and ¼ cup of sugar to make a sticky mixture.  Apply the mixture to both sides of each paper strip.  Hang the strips near your dog’s food and water bowls (high enough so the dog cannot grab them).  Replace the strips when they have several dead flies on them. Pour apple cider vinegar into a bowl, cup, glass, etc.  Place plastic wrap over the top of the bowl, cup, glass, etc., and attach it using an elastic.  Make sure the plastic is pulled tight over the opening, like the surface of a drum.  Using a toothpick, stab a bunch of holes into the plastic wrap.  Place the whole contraption near your dog’s food and water bowls, but not in a location where the dog can get to it.  Empty and refill as often as needed. An alternative to apple cider vinegar is wine.  Wine can be used in the exact same fashion to attract and kill flies.  You can also add dish soap to the wine to help ensure the flies cannot escape.  Of course, you’d have to waste wine in order to do this, so your problem would probably have to be rather severe to use this method! Cut an individual-sized pop/soda/juice bottle in half, making the bottom half larger than the top half.  Fill half the bottom half with water and a put in a couple drops of dish soap.  Place the top half of the bottle into the bottom half, inverted (i.e. the opening of the bottle goes towards the water, without the cap on).  Spread honey or jam near the mouth of the bottle that’s facing the water.  Place the whole contraption near your dog’s food and water bowls - but still out of their reach (as it’ll probably attract dogs as well as flies!). A bug zapper is designed more for outdoor use than indoor use and requires an electrical outlet.  The zapper emits a light that attracts many insects and when they get close...

TL;DR in Vietnamese:
Tự làm giấy bẫy ruồi. Bẫy ruồi giấm bằng giấm táo. Bẫy ruồi bằng mật ong hoặc mứt. Mua và lắp đèn bẫy côn trùng.