diff --git a/common/mise.root.toml b/common/mise.root.toml
index c270a9e..150a63e 100644
--- a/common/mise.root.toml
+++ b/common/mise.root.toml
@@ -34,6 +34,10 @@ lockfile = true
 interactive = true
 run = "docker compose -f compose.dev.yaml up --remove-orphans"
 
+[tasks.secrets]
+description = "scan the whole history for secrets"
+run = "gitleaks git --redact --no-banner"
+
 [tasks."dev-down"]
 run = "docker compose -f compose.dev.yaml down --remove-orphans"
 
diff --git a/lib/publish.sh b/lib/publish.sh
index a09955d..9061957 100644
--- a/lib/publish.sh
+++ b/lib/publish.sh
@@ -120,6 +120,31 @@ main_is_protected() {
   gh api "repos/${1}/rulesets" --jq '.[].name' 2>/dev/null | grep -qx main
 }
 
+# enable_secret_scanning <slug>
+# GitHub scans and blocks the push itself. Free on a public repository; on a
+# private one it needs Advanced Security, which answers 422 — the same shape
+# protect_main handles, and reported the same way.
+enable_secret_scanning() {
+  local response status=0
+
+  response="$(gh api -X PATCH "repos/${1}" --input - 2>&1 <<'EOF'
+{
+  "security_and_analysis": {
+    "secret_scanning": { "status": "enabled" },
+    "secret_scanning_push_protection": { "status": "enabled" }
+  }
+}
+EOF
+)" || status=$?
+
+  [ "$status" -eq 0 ] && return 0
+  case "$response" in
+    *"Advanced Security"*|*"not available"*|*"upgrade"*|*"Upgrade"*) return 2 ;;
+  esac
+  printf '%s\n' "$response" >&2
+  return 1
+}
+
 # set_release_secrets <slug>
 # Optional on both sides: the release workflow declares them optional and falls
 # back to GITHUB_TOKEN. What the fallback costs is a release pull request whose
diff --git a/scaffold b/scaffold
index 5793c61..2ed44b3 100755
--- a/scaffold
+++ b/scaffold
@@ -712,6 +712,7 @@ cmd_publish() {
     fi
 
     log "would allow Actions to open pull requests on ${slug}"
+    log "would enable secret scanning and push protection"
 
     if [ "$protect" -eq 1 ]; then
       if main_is_protected "$slug"; then
@@ -739,6 +740,14 @@ cmd_publish() {
   allow_actions_to_open_pull_requests "$slug"
   log "Actions may open pull requests (Release Please needs this)"
 
+  local scanning=0
+  enable_secret_scanning "$slug" || scanning=$?
+  case "$scanning" in
+    0) log "secret scanning and push protection are on" ;;
+    2) warn "no secret scanning: it needs Advanced Security on a private repository. The CI scan still runs on every push" ;;
+    *) die "could not enable secret scanning on ${slug}" ;;
+  esac
+
   if [ "$protect" -eq 1 ]; then
     if main_is_protected "$slug"; then
       log "main already has a ruleset — left alone"
diff --git a/tests/publish.bats b/tests/publish.bats
index b328395..209feff 100644
--- a/tests/publish.bats
+++ b/tests/publish.bats
@@ -17,8 +17,8 @@ teardown() {
 # creating a repository on anybody's account. Same technique as the curl and
 # docker stubs in tests/install.bats.
 #
-# GH_SCENARIO: `absent` (no such repository), `exists`, or `plan-limit` (a
-# repository that exists on an account whose plan refuses rulesets).
+# GH_SCENARIO: `absent` (no such repository), `exists`, `plan-limit` (an
+# account whose plan refuses rulesets), or `no-advanced-security`.
 _stub_gh() {
   local bin="${WORKDIR}/stub"
   mkdir -p "$bin"
@@ -38,6 +38,12 @@ esac
 # `gh api repos/<slug>/rulesets` with no -X is the listing; with -X POST it is
 # the create.
 case "$*" in
+  *"-X PATCH"*)
+    if [ "${GH_SCENARIO}" = no-advanced-security ]; then
+      echo 'gh: Advanced Security is not available for this repository (HTTP 422)' >&2
+      exit 1
+    fi
+    exit 0 ;;
   *"-X POST"*rulesets*)
     if [ "${GH_SCENARIO}" = plan-limit ]; then
       echo 'gh: Upgrade to GitHub Pro or make this repository public to enable this feature. (HTTP 403)' >&2
@@ -125,7 +131,7 @@ _project() {
   [[ "$output" == *"would allow Actions to open pull requests"* ]]
   [[ "$output" == *"would protect main"* ]]
 
-  run grep -cE 'repo create|-X PUT|-X POST|secret set' "$GH_LOG"
+  run grep -cE 'repo create|-X PUT|-X POST|-X PATCH|secret set' "$GH_LOG"
   [ "$output" = 0 ] || { echo "a dry run called:"; cat "$GH_LOG"; false; }
 }
 
@@ -170,6 +176,33 @@ _project() {
   [ "$output" = 1 ]
 }
 
+@test "publish turns on GitHub's own secret scanning" {
+  # The control that blocks a secret at push time, before it lands. Free on a
+  # public repository; the CI scan covers the private case.
+  _stub_gh
+  _project
+
+  GH_SCENARIO=exists run scaffold publish "$PROJECT"
+  assert_ok
+  [[ "$output" == *"secret scanning and push protection are on"* ]]
+  run grep -c -- '-X PATCH repos/acme/demo' "$GH_LOG"
+  [ "$output" = 1 ]
+
+  # The payload travels on stdin, so it is checked where it is written.
+  run bash -c "sed -n '/\"security_and_analysis\"/,/^EOF\$/p' '${SCAFFOLD_ROOT}/lib/publish.sh' \
+    | grep -c 'secret_scanning_push_protection'"
+  [ "$output" = 1 ]
+}
+
+@test "a plan without Advanced Security is a warning, not a failed publish" {
+  _stub_gh
+  _project
+
+  GH_SCENARIO=no-advanced-security run scaffold publish "$PROJECT"
+  assert_ok
+  [[ "$output" == *"no secret scanning"* ]]
+}
+
 @test "a plan that refuses rulesets is a warning, not a failed publish" {
   # Measured against a real repository: a private repository on a free account
   # answers 403 "Upgrade to GitHub Pro". Everything before it succeeded, and