^ What Jester said. 5 out of the 6 dogs in my pack are intact males. Any of them would've skewered me alive by now with their os bones if I let them run roughshod. Peritonitis is a thing. Think its bad in a vagina? Try taking a rimshot of a baculum stab on the anus! Searing, throbbing, blinding-white pain. Sink down to the bed and cry out. Sex suddenly becomes unthinkable. Tho I will admit even this has diminished with time & practice -- if I slip up and let it happen at all. Where it used to take a whole day to recover from that, now I can be back in action in a few minutes. A few minutes of miserable writhing, cussing, grinding clenched teeth, har har. Likewise when I was 18, green, and gung-ho to give my first fellatio to a dog, I had no idea what was coming. I just gave him my whole mouth to thrust. On his very first lunge inside, he stabbed me with such force of a sharp os, landing straight into/across my tongue. Tears welled and that tongue thickened & swelled so bad I couldn't talk or chew for days after. I didn't try that shit again for months. No thanks. That's not good sex for any of us.
Instead, I worked on perfecting a system of training them to expect a guiding hand, and then I line us up back there so they cannot stab anywhere off the mark. I did this by holding them on me up there and not letting them dismount when their efforts don't succeed. This teaches patience, gets them to expect a helping hand to get their reward. Our system works flawlessly -- unless I don't reach around & catch them in time, har har.
Our routine goes something like: roughhouse with them to get 'em riled up and in the mood. Lot of scent foreplay, oral teasing, rimming, and building up their erections. Edging, jacking & tugging their sheathed bulbs as they harden and fill out beautifully, then those erections subside, then repeat. Lube myself and my hands liberally, and get into position for him. Here I give another tease as a compromise: let them hop up and stab me around a few times, doing their exploratory thrusts, but I very carefully duck their aims and keep my tender asshole out of harm's way (lol). Allow them to dismount after a few unproductive thrusts. Make the invitation again, mount up, duck the thrusts, dismount. Repeat this several times. I feel this type of foreplay best mimics normal dog-on-dog mating; they don't usually achieve intromission to the bitch's vagina on the first try either, so I let them have the same fun with me. Its familiar for them, serves as a good final line of foreplay, and works their libido to that last mile of fever pitch.
And when at last its time for the real one... they feel my hand back there and they all know to stop, stand stock still, not dismount me, and wait patiently for the guiding hand to do its thing. I reach around behind, pull the sheath back and line up their tips either right at--or preferably just inside of--my lubed opening. Getting that tip inside, say even a 1/4", is ideal. It'll still work if they're perfectly lined up just outside me, but I'd much rather know for certain that they've already got the tip inside. Soon as they feel that, I let go the bull and he charges out of that gate with fury! Meanwhile I change my grip to double handfuls of sheets or the edge of the bed, bite a mouthful of pillow, let my eyes roll back in my head, and hold on for the ride
. But refusing him the chance to mount if he goes that hard. Think of a dog that snaps fingers when given a treat. You can teach them to take it "easy". 