Both SimpleVault and Safe guards compile

contracts/guard/src/GuardV0.sol

@@ -8,15 +8,32 @@ pragma solidity ^0.8.0;
 import "@openzeppelin/access/Ownable.sol";
 import "./lib/Path.sol";
 import "./IGuard.sol";
+import "./GuardV0Base.sol";
 
 /**
  * Prototype guard implementation.
  *
  * - Hardcoded actions for Uniswap v2, v3, 1delta
  *
  */
-contract GuardV0 is IGuard, GuardV0Base, Ownable {
+contract GuardV0 is GuardV0Base, Ownable {
 
     constructor() Ownable() {
     }
+
+    /**
+     * Specify a modifier for guard owner
+     */
+    modifier onlyGuardOwner() override {
+        require(owner() == _msgSender(), "Ownable: caller is not the owner");
+        _;
+    }
+
+    /**
+     * Get the address of the proto DAO
+     */
+    function getGovernanceAddress() override public view returns (address) {
+        return owner();
+    }
+
 }

contracts/guard/src/GuardV0Base.sol

@@ -11,10 +11,12 @@ import "./IGuard.sol";
 /**
  * Prototype guard implementation.
  *
- * - Hardcoded actions for Uniswap v2, v3, 1delta
+ * - Hardcoded actions for Uniswap v2, v3, 1delta, Aave
+ *
+ * - Abstract base contract to deal with different ownership modifiers and initialisers (Safe, OpenZeppelin)
  *
  */
-abstract contract GuardV0Base {
+abstract contract GuardV0Base is IGuard  {
     using Path for bytes;
     using BytesLib for bytes;
 
@@ -247,10 +249,19 @@ abstract contract GuardV0Base {
         allowAsset(token, notes);
     }
 
+    // Satisfy IGuard
     function validateCall(
         address sender,
         address target,
         bytes calldata callDataWithSelector
+    ) external view {
+        _validateCallInternal(sender, target, callDataWithSelector);
+    }
+
+    function _validateCallInternal(
+        address sender,
+        address target,
+        bytes calldata callDataWithSelector
     ) public view {
 
         if(sender == getGovernanceAddress()) {

contracts/guard/src/IGuard.sol

@@ -1,5 +1,9 @@
 pragma solidity ^0.8.0;
 
 interface IGuard {
-    function validateCall(address sender, address target, bytes memory callDataWithSelector) external;
+
+    /**
+     * Revert if the smart contract call is not allowed
+     */
+    function validateCall(address sender, address target, bytes memory callDataWithSelector) external view;
 }

contracts/guard/src/MockGuard.sol

@@ -15,7 +15,7 @@ contract MockGuard is IGuard {
         address sender,
         address target,
         bytes calldata callDataWithSelector
-    ) external view {
+    ) public view {
         // Don't revert
     }
 

contracts/safe-integration/src/TradingStrategyModule.sol

@@ -66,7 +66,7 @@ contract TradingStrategyModule is Module, GuardV0Base {
 
         // Check that the asset manager can perform this function.
         // Will revert() on error
-        validateCall(msg.sender, target, callData);
+        _validateCallInternal(msg.sender, target, callData);
 
         // Inherit from Module contract,
         // execute a tx on behalf of Gnosis