The premise of the question is flawed. The "best way" is to ensure secrets are never *in* the code to begin with. Treating the repository as the security boundary for secrets is a failure of the supply chain model. The focus must shift to credential injection at deployment, backed by attestation.

A hardened pattern requires three layers:

1. **Pre-commit Tooling**: Use static analysis to block commits containing potential secrets. This is a guardrail, not a solution.
```bash
# Example: Using gitleaks in a pre-commit hook
# .pre-commit-config.yaml
repos:
- repo: https://github.com/gitleaks/gitleaks
rev: v8.18.0
hooks:
- id: gitleaks
```

2. **Runtime Secret Injection**: Secrets must be provided to the application via a secure, auditable channel at runtime. This decouples the secret from the code artifact.
* Use a secrets manager (e.g., Vault, AWS Secrets Manager).
* For containers, use ephemeral secrets mounted as files or provided via environment variables from a secure runtime (e.g., a sidecar).

3. **Attestation and Policy Enforcement**: This is the critical layer. You must cryptographically verify the *provenance* of the code and the *integrity* of the deployment environment before secrets are released. The deployment system must attest that it is running the exact, approved artifact from your CI/CD pipeline in the intended environment.

The OpenClaw Rust-Agent prototype demonstrates this by generating an in-toto attestation for a container build, which a policy engine can evaluate before allowing a workload to access a secret. The secret is never stored with or in the code; it is released only to attested workloads.

Without this attestation layer, you're relying on perimeter security for your supply chain, which we know is insufficient.