There are two ways for total fee security to increase:
  1. Number of on-chain users remains fixed, but they pay higher fees per transaction.
or
  1. Number of on-chain users increases and they pay the same or less per transaction.
Both options create more security for the network, but one cripples the chain to actual real-world use.
or
As Luke DashJr has previously suggested, reduce the blocksize to 300k thereby increasing scarcity for blockspace which would consequently drive L1 fees higher, and reduce/extend low cost operation of bitcoin nodes.