For any project, layers of security are crucial. Audits represent one layer, while core developers and contributors collaborate to provide many more. Notable security programs, designs, and partners beyond audits include:

Embedded security researchers via Asymmetric Research
Attackathon programs in partnership with Immunefi
sBTC’s decentralized network of validators/signers (removing the need to entrust a single entity and mitigating counterparty risk)
Stacks’ underlying design that offers 100% Bitcoin finality, securing sBTC at the consensus level of a $2.5 billion network.
Support at the app layer via Hypernative
Bitcoin L2 Labs' whitehat security program
Stacks Foundation's partnership with Staking Defense League,
Stacks Founation's ongoing Immunefi bug bounty program
Dedicated Stacks Foundation Residents focused exclusively on fuzz and penetration testing (created Rendezvous)