How to bury my dog? How deep must I dig?

She is only just dead this morning, I awoke to an awful stench. My deceased father use to bury our animals when they died and I did not want to go to the specific spot he did it as I did not want to hit the other ones but I remembered this flowerbed areahe had dug up many many years before and thought that would be a good area, no flowers in it anymore near a banana tree that is dead. I have my dog, a chihuahua in a sturdy box and I have dug a hole about two feet and this is where the earth got too hard for me to dig, I can't make much of a dent in it. It has been a long time since I last saw a hole dug for a dead animal but I think this is as deep as my father went before though I believe it is customary to dig three feet. Is two feet ok? her box is about 4 inches high.