diff --git a/.github/workflows/luacheck.yml b/.github/workflows/luacheck.yml
new file mode 100644
index 0000000..f24a4b0
--- /dev/null
+++ b/.github/workflows/luacheck.yml
@@ -0,0 +1,18 @@
+name: luacheck
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+    - uses: actions/checkout@v2.3.4
+    - name: apt
+      run: sudo apt-get install -y luarocks
+    - name: luacheck install
+      run: luarocks install --local luacheck
+    - name: luacheck run
+      run: $HOME/.luarocks/bin/luacheck ./
diff --git a/.luacheckrc b/.luacheckrc
index 2467b80..0a8ecb7 100644
--- a/.luacheckrc
+++ b/.luacheckrc
@@ -1,8 +1,4 @@
-unused_args = false
-allow_defined_top = true
-
 globals = {
-	"minetest",
 	"spacecannon"
 }
 
@@ -12,7 +8,7 @@ read_globals = {
 	table = {fields = {"copy", "getn"}},
 
 	-- mod deps
-	"technic", "default",
+	"technic", "default", "digilines",
 
 	-- Minetest
 	"minetest",
diff --git a/cannon.lua b/cannon.lua
index b07306e..8817157 100644
--- a/cannon.lua
+++ b/cannon.lua
@@ -49,7 +49,7 @@ local register_spacecannon = function(def)
 			if goes_through then
 				local objs = minetest.get_objects_inside_radius({x=pos.x,y=pos.y,z=pos.z}, 1)
 				local collided = false
-				for k, obj in pairs(objs) do
+				for _, obj in pairs(objs) do
 					if obj:get_luaentity() ~= nil and obj:get_luaentity().name ~= self.name then
 						collided = true
 						obj:punch(self.object, 1.0, {
@@ -72,7 +72,7 @@ local register_spacecannon = function(def)
 			end
 		end,
 
-		on_activate = function(self, staticdata)
+		on_activate = function(self)
 				minetest.after(def.timeout,
 					function(me)
 						me.object:remove()
@@ -103,7 +103,7 @@ local register_spacecannon = function(def)
 		legacy_facedir_simple = true,
 
 		mesecons = {effector = {
-			action_on = function (pos, node)
+			action_on = function (pos)
 				spacecannon.fire(pos, def.color, def.speed, def.range)
 			end
 		}},
@@ -140,7 +140,7 @@ local register_spacecannon = function(def)
 			spacecannon.update_formspec(meta)
 		end,
 
-		technic_run = function(pos, node)
+		technic_run = function(pos)
 			local meta = minetest.get_meta(pos)
 			local eu_input = meta:get_int("HV_EU_input")
 			local demand = meta:get_int("HV_EU_demand")
@@ -159,7 +159,13 @@ local register_spacecannon = function(def)
 			end
 		end,
 
-		on_receive_fields = function(pos, formname, fields, sender)
+		on_receive_fields = function(pos, _, fields, sender)
+			local playername = sender and sender:get_player_name() or ""
+			if minetest.is_protected(pos, playername) then
+				-- only allow protection-owner to fire and configure
+				return
+			end
+
 			local meta = minetest.get_meta(pos)
 
 			if fields.fire then
@@ -219,7 +225,3 @@ register_spacecannon({
 	desc = "slow, heavy damage",
 	ingredient = "spacecannon:cannon_yellow"
 })
-
-
-
-
diff --git a/digiline.lua b/digiline.lua
index 03f1dd6..3f47e96 100644
--- a/digiline.lua
+++ b/digiline.lua
@@ -10,7 +10,7 @@ spacecannon.digiline_rules = {
 	{x= 0,y= 1,z= 0},{x= 0,y=-1,z= 0}, -- along y above and below
 }
 
-spacecannon.digiline_handler_get = function(pos, node, channel, msg)
+spacecannon.digiline_handler_get = function(pos, node, channel)
 	local meta = minetest.get_meta(pos)
 
 	local input = meta:get_int("HV_EU_input")
@@ -31,7 +31,7 @@ spacecannon.digiline_handler_get = function(pos, node, channel, msg)
 	digilines.receptor_send(pos, spacecannon.digiline_rules, channel, resp)
 end
 
-spacecannon.digiline_handler_fire = function(pos, node, channel, msg)
+spacecannon.digiline_handler_fire = function(pos, node, channel)
 	local meta = minetest.get_meta(pos)
 
 	-- TODO: Add ability to set "target node" in the msg, and if its within
diff --git a/util.lua b/util.lua
index 912e58f..3315dc7 100644
--- a/util.lua
+++ b/util.lua
@@ -27,11 +27,13 @@ spacecannon.update_formspec = function(meta)
 	end
 end
 
-spacecannon.can_shoot = function(pos)
+spacecannon.can_shoot = function()
+	-- arguments: pos
 	return true
 end
 
-spacecannon.can_destroy = function(pos)
+spacecannon.can_destroy = function()
+	-- arguments: pos
 	return true
 end
 
@@ -173,5 +175,3 @@ spacecannon.facedir_to_down_dir = function(facing)
 		{x=1, y=0, z=0},
 		{x=0, y=1, z=0}})[math.floor(facing/4)]
 end
-
-