About the genitive form of the word "Hund"
I am a bit confused over how to change the word "Hund" into it's genitive form. I wrote "That is the dog's ball. - Das ist der Ball des Hunds."
One person has said it's correct, but another person has said it should be Das ist der Ball des Hundes.
The reason I am confused, is, well, firstly I have had two different answers. Secondly, If I add "es", does this not mean Hund (dog) has become Hunde (dogs) and therefore it should be Das ist der Ball der Hunde? Thirdly my dictionary shows the genitive form as Hund(e)s, so I have read that to mean, in the singular it is "Hunds" and in the plural "Hunde"
How exactly do you turn the SINGULAR of "Hund (DOG)" into it's genitive form, by adding "s" or by adding "es"?