No investment is 100% safe but those bonds are as close as you are going to get. The taxes and bonds on a property do not go away when a house goes into foreclosure, they accrue interest and penalties and must be paid back when the bank sells the house or land, the transfer cannot take place until it is paid in full and if it isn’t paid in full for five years the county will take the property. Nobody is better at making sure it gets paid than the county assesor, mello roos cannot be negotiated down like the value. The ways that you can get screwed out of your investment are things like nuclear war, California falling into the ocean, or anything else that would make the land vanish and become inhabitable forever. The odds are in your favor.