In college, rented a 4 bedroom house with 2 other guys. Fenced yard. Pretty nice place. One of the roomies had a buddy get kicked out of his apartment because of his dog. 1/2 Pit, 1/2 Great Dane. Sinbad. He was as tall as a Dane and built like a pit. I'd guess that dog was 185 lbs. I was about 205 muscled up and lean then. Roomie took in the dog but I took care of him. He was a big pussy, real lovable dog but he looked absolutely ferocious. He hated squirrels with a passion because they would steal his food and then taunt him from a limb too high for him to reach.
I ran 3-10 miles almost every day then and had a long swingset type chain on a choke collar for Sinbad. I took him almost every run. I had to be paying attention because if he thought he might be able to nab a squirrel, he'd go for it.
When we first took him in, the mail lady stopped delivering. She was maybe 61" tall and 110 lbs. Sinbad would stand up on the fence with his front legs and tell her his name was Sinbad. I don't blame her. I caught her one day and introduced her to Sinbad and she gave him a treat. No problem after that.
He would jump that 4' fence without even touching it. I'd come home and see him going back into the back yard. Neighbor said Sinbad would jump the fence everyday as soon as my car was a block down the road and then he'd spend the rest of the day on the porch, going back over to get a drink or a snack. He'd also jump back when our postwoman would walk a few houses up and wait, barking, for his treat.
I never saw him be aggressive except after squirrels until one day I took a different route on my run. Yard had a real nice 8' chainlink fence and inside were some real specimens. A huge Rot, an almost completely black GSD and a nearly blond Doberman female. GSD was mauling the fence, Rot was standing up on the fence and bouncing it with his front feet. Lady dog was standing back and barking. Ol' Sinbad stops, looks, his hair stood up and walked to the fence real stiff legged even while I was pulling on him. He sniffs the GSD, took a half step and hiked his leg and pissed right on that dogs head. GSD shut right up and backed away. Sinbad threw some grass and went to the Rot, walked back and forth a couple of times and then jumped and hit that fence so hard that it knocked the Rot down. Rot jumps right back up and started to go for the fence and Sinbad let out a growl...I had never heard him growl before. Rot just stood there then barking. I was finally able to pull Sinbad away but he looked back for a block.
I told my buddy that we needed to get rid of this dog before he twisted off at the wrong time. Someone walking a dog by that wanted to act aggressive or something. If not for that nice fence, there is no way I would have been able to stop those 4 dogs from going at it and I don't think it would have been a pretty sight. He was sent to live the original owners dad.
I have had bird dogs all of my life and since I met my current wife, we have had mini Dachshunds. I've only had one bird dog that I would consider slightly aggressive, other than the prey drive. They've all been cat killers and a dead skunk or rabbit or something on the porch is not uncommon. I am sure to socialize them with other dogs and people because I hate a fucking aggressive bird dog attacking someone elses bird dog before or during a hunt. I've loaded back up and not hunted because of someone elses fucking dog.
These little weiner dogs, though, they are sure lovers of the family but these little dogs are aggressive. They have zero fear of anything and go right in. They don't know they only weigh less than 13 pounds or just don't care. I think weiner dogs are high on the list of most likely to bite.