Ok, hear me out: Even though interspecies breeding is unrealistic, a lot of times in nature when the sperm of one species enters in contact with the egg of another one, both are destroyed in the incompatibility. And since those eggs are the possible future child of that species, they wouldn't want to lose them.

So, my idea is, having dragons use their own semen as a method of defense, if anyone reaches nearby them to attack, they immediately cum a giant load into them, which not only the target would want to avoid to not get it's eggs destroyed, but could potentially also slow them by it's thick consistency.

"But what about males? This method would only protect against half of the possible attackers!" You ask. Well, the thing is that, just like humans, sperm isn't liberated alone, semen is also expelled to help them reach its target, but dragon's semen would also contain an incredibly potent aphrodisiac, and any male who enters in contact with it, would want to relieve themselves, not only losing their own sperm, but also, losing a good amount of time masturbating.

"But how will the dragons expell so much cum?" This is the best part, because, these dragons would have six big dicks (because bestagons) that can produce immense amounts of cum, and they would be able to slightly move them for aiming, being able to protect themselves from all sides at once.

Finally, humans could also potentially try to domesticate them for their potent aphrodisiac, being able to be used both in their skin, but also by drinking.