Is there a tried & true DIY weed killer to use around the house?

You can use basic vinegar!

I use round up .

I fill a spray bottle with vinegar and add two squirts of dish detergent Spray during the hottest part of the day. It will take a few days for the weeds to die but this works great.

We always use "Round-Up". mix with water & spray away with your pump sprayer or.....

I use roundup and various vinegar recipes . They work, but weeds they always find a way. I put down 5 inches of cedar mulch and the weeds will grow in the mulch duct or in the mulch itself. I take my mulch every so many days and apply preen. Although, I often feel like I'm not making a difference.