Трахать is obviously not a good translation of "to hump" when describing what dogs do. It's not a polite word and can't be used in print, wherеаs "to hump" is perfectly harmless and can be used by parents in front of kids, etc. Is there a "nice" word for this in Russian?
Edit: All the translations suggested so far miss the fact that dogs hump outside of regular intercourse or mating. So while it's possible to use a euphemism like "Он пристает к игрушкам," that doesn't come across as clearly as "He humps his toys" and many listeners might miss the meaning.
And what about "Doctor, he keeps humping my boyfriend's leg, it's so embarrassing"? Humping is literally the act of thrusting the pelvis toward something, and it's puzzling that there isn't an equivalent transitive verb in Russian. Especially since Russian dogs hump a lot more as neutering is not very popular there.