This is a question that I've encountered from clients multiple times, most of the time it's by people with little knowledge of PPC, who are in highly competitive fields but on very tight budgets, and who tend to be more than a little paranoid. It's also usually from people who would personally do exactly the same thing to their competition. However, that's not to say that irrelevant, malicious clicks can never be a problem.
Google themselves have strong filters in place to flag such clicks as irrelevant. As such, you're either not charged at all or automatically refunded for these. You can see the clicks Google are flagging themselves as irrelevant in your Google Ads interface.
...add the invalid interaction data columns to your campaign statistics table to see the number and percentage of invalid interactions in your account.
As that page also mentions, if you feel that these filters aren't stopping malicious clicks on your ads, you can report these to Google yourself. It links off to a whole separate page where Google outlines what steps you can take to both identify invalid clicks and how to stop them or report them to Google to get a refund.
Aside from that, there are third-party services which can monitor your traffic and automatically report invalid clicks on your behalf. Whether you want to pay for these would depend on how much money you believe you are losing. I personally have never used any of these, but a quick Google search for, "stop competitors clicking adwords," will give you plenty of options to research yourself.