You create tamper-proof node software. Seriously, I have been working on this for years and have thought long and hard about the how to deal with the unique security context problem of a permissionless (i.e. open) P2P network overlay forming a single computer abstraction. And then I implemented it. Too much to get into here but I assure you I address it at length in the whitepapers. Take a look at the UnoSys paper on the website for the gory details. Here's the link: https://worldcomputer.org/whitepapers