My Dog Has Black Smelly Guck In His Ears, What Is It And What Can I Do For It

This is called ear canker. Some sort of irritant - which could be an infection, is causing over-production of ear wax. The build up needs to be cleaned out. There are special wipes you can buy, but I use the ones they make for babies and these work well. Cover your little finger with the wipe (or a cotton bud if you are squeamish) and start cleaning it out, starting with what is easiest to reach.
This is itchy for the dog and it will probably squirm, but will feel better when you have finished. If the stuff smells bad, or the skin is red, you will need some drops from the vet.

It's probably an ear infection. You can try using a soft damp washcloth and wipe the ear. DO NOT dig in the ear! This could injure it. My vet told me to use a solution of white vinager/rubbing    alcohol equal parts.

Probably an ear infection. Does it hurt him when you scratch it? These things can usually be cleared up with some drops and wash. Although there are some breeds of dogs (such as Cocker Spaniels) that have these ear problems all their life.

My dad's chesapeake had the same thing and it turned out to be a yeast infection in her ear...you can get over the counter ear cleaners at any pet supply store...but you may need to see your vet for something to get rid of the yeast

It could be ear mites or just infection take the dog to your vet as if its ongoing maybe worth getting canural ear drop it helped my dogs in the past.