The important thing to remember is that, with all investment advice, you must consider the source. Keep in mind that even professional money managers rarely beat the market, so imagine
how much more difficult it is for an amateur to do so -- especially with an unproven "hot tip."
Of course, even a broken clock is right twice a day, and every now and then one of these investments may prove to be worthwhile -- but usually they aren't worth considering. Remind your dad that his golfing buddies and neighbors probably aren't telling him about all the investments they've chased that turned out to be busts or, even worse, outright scams.
Try to explain to your father that investing in general should be done as a part of a thoughtful plan of asset allocation -- this is the only way to consistently make money. Chasing after hot tips never works, because so-called hot stocks inevitably cool down by the time amateur investors learn about them. It may be less exciting than a get-rich-quick scheme, but most investors are better off by far with a low-cost, low-fee index mutual fund with a proven track record of success.
If he won't listen to your arguments, you might consider taking him to meet with an accountant, broker, or financial planner to talk about better investment options. Sometimes parents are more amenable to what a professional has to say -- even if it's the exact same advice you've been giving.
But if he won't listen to reason or visit a financial advisor, there's unfortunately not much you can do about his money choices -- barring extreme and divisive legal measures, like appointing a court conservator. As long as he's mentally competent, you don't have any legal rights or say as to what he should do with his money.