The secret to leaving a dog alone all day is to keep them occupied, also which breed you get is important. Working dogs are a no-no as they will use their unspent energies in destructive ways. If you have a large garden then a dog run and kennels is a good idea as long as they don't bark all day.
Pug's suffer from numerous health problems and require alot of looking after whereas a Shar-Pei is quite content to be in it's own company and generally don't bark alot.
We have had a single dog for years but recently bought another to keep it company and you can tell that the dog is much happier.