How do I set up erase and secure?

My phone was stolen so I tried to erase from Samsung Device Manager but it just sends an erase instruction which I don't know whether the person who turns my phone on will be able to just stop from the device or not :( Also the erase button on google device which sends a notification to the stolen phone to set up, the friendly thief ;) So I'm trying to not be in the same position again, I don't understand how to set up erase and secure from my new device. Please help, Thanks