Why has my dog been squirting?

I have a 3 year old pure German Shepard. He is a great dog besides the fact that every time anyone comes in the house (even our family) he will squirt a liquid (urine? maybe?) everywhere. It smells very fishy and he will smell it after. I’m not sure what this is since he is/has been trained since being a puppy… He never pees or poops in the house either. Only when he gets excited he squirts this mysterious liquid.