When I was a teen I had a female Canine lover, but as she got older she was not always receptive to my desires and I would look to neighbors dogs to engage with.
One on occasion, I had played with a young male mixed dog named Jox. His "Owners" saw how well he got along with me (because I had sucked him off a few times before) and let me take him out for walks. I noticed him trying to get to female dogs in the neighborhood on one of these walks and as a horny teen I decided to let him make me his bitch. I had taken a Knot before so I was ready and psychologically prepared to do it again, we headed to an open not so populated area of open field that separated our neighborhood from a business section of town. It had some thick trees in one spot that blocked us from both the businesses and the houses, I stripped down for him and let explore my nakedness as I was petting and praising him.
I didn't take long after that for him to mount me and we fucked for a about 10 to 15 minutes, mostly him getting into a good stance and to find my hole. But once he prodded me into submission and found my now aching hole, he entered me and we fucked for sometime with him either falling out of me or his Knot fulling reaching my hole. But soon as he Knotted me and we Tied together it was heaven, I moaned and groaned as he engorged my anus. I would reach back and pet him to let him know that he was doing great, hopefully my moans of pleasure told him he was doing something right. We stayed Tied for sometime as I jacked off and he dismounted me to stand ass to ass, I don't if somebody was passing nearby or had seen us. But he would bark and pull from to try and explore or go in a specific direction, he ended up pulling out of me in a gloriously painful last tug and I collapsed onto my side. I tried my best to keep his seed inside me and laid in passionate relief as he cleaned himself and wandered around to explore.
His "Owners" never suspected a thing and he became more attatched to me after our first Tie and we would get together to fuck more after that, not as often as I wanted back then but often enough to be satisfied.