How to secure a Linux node running satoshi 0.16.1?
As a quick answer, some wallets allow you to specify a node that they will connect to. You can run your own node, and point your wallet at it. Beyond being trustless, this has an added bonus of increasing your financial privacy, especially if your node is connected to the tor network. 

Note that many such wallets are ‘light wallet’ mobile applications, but I would trust a mobile wallet over a desktop full node wallet myself. This offers a good solution of maintaining sovereignty for a day-to-day use wallet in my opinion. 

For larger amounts, using a HW wallet or other cold storage mechanism is highly recommended!