Hmm.... sounds really weird. Wait.. YOU'RE GOING FOR ROD TOO?! He's minee! xD Anyways, if you're still dating Allen, i don't think you can encounter Rod's heart event. For his black heart event, » Rod's house » 1:00 pm to 6:00 pm » Friday, Saturday, or Sunday » Any weather » You are playing as the girl main character » Rod has 5000 Friendship Points or more » You own at least 1 Chicken If this doesn't work, tell me and i'll do some more research for yah!
Also, if he's never home, wait for a rainy or snowy day! Go to his house around 1 PM because he'll still be eating by then. After 1 PM, i believe he'll be somewhere else. Chances are, sometimes he'll just stay home.
Unfortunately I'm not really sure. None of my friends went after Rod, and I haven't even gotten any of his heart events myself, because he never seems to be home. I suppose you'll just have to wait for a rainy day.