As far as you can fit your finger inside the
ear, you will NOT hit the
ear drum. The
ear drum is actually at a sharp right angle
in towards the brain, so the ear canal will look like it just goes in a slight downward incline, but at the end, it takes a sharp turn. So as long as you shoot the stuff in the same angle as the ear canal, you will not damage anything.
When you do put anything wet and cold in your dogs ear, it will try to jerk away and shake it out. Wouldnt you?