diff --git a/lib/model.js b/lib/model.js
index c112a8e..9638af5 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -99,8 +99,10 @@ function deserialize (rawData) {
 
 /**
  * Deep copy a DB object
+ * The optional strictKeys flag (defaulting to false) indicates whether to copy everything or only fields
+ * where the keys are valid, i.e. don't begin with $ and don't contain a .
  */
-function deepCopy (obj) {
+function deepCopy (obj, strictKeys) {
   var res;
 
   if ( typeof obj === 'boolean' ||
@@ -113,14 +115,16 @@ function deepCopy (obj) {
 
   if (util.isArray(obj)) {
     res = [];
-    obj.forEach(function (o) { res.push(deepCopy(o)); });
+    obj.forEach(function (o) { res.push(deepCopy(o, strictKeys)); });
     return res;
   }
 
   if (typeof obj === 'object') {
     res = {};
     Object.keys(obj).forEach(function (k) {
-      res[k] = deepCopy(obj[k]);
+      if (!strictKeys || (k[0] !== '$' && k.indexOf('.') === -1)) {
+        res[k] = deepCopy(obj[k], strictKeys);
+      }
     });
     return res;
   }
diff --git a/test/model.test.js b/test/model.test.js
index ac642ed..bc92e4f 100644
--- a/test/model.test.js
+++ b/test/model.test.js
@@ -260,6 +260,22 @@ describe('Model', function () {
       b[0].hello.should.equal('another');
       a[0].hello.should.equal('world');      
     });
+    
+    it('Without the strictKeys option, everything gets deep copied', function () {
+      var a = { a: 4, $e: 'rrr', 'eee.rt': 42, nested: { yes: 1, 'tt.yy': 2, $nopenope: 3 }, array: [{ 'rr.hh': 1 }, { yes: true }, { $yes: false }] }
+        , b = model.deepCopy(a)
+        ;
+        
+      assert.deepEqual(a, b);
+    });
+    
+    it('With the strictKeys option, only valid keys gets deep copied', function () {
+      var a = { a: 4, $e: 'rrr', 'eee.rt': 42, nested: { yes: 1, 'tt.yy': 2, $nopenope: 3 }, array: [{ 'rr.hh': 1 }, { yes: true }, { $yes: false }] }
+        , b = model.deepCopy(a, true)
+        ;
+        
+      assert.deepEqual(b, { a: 4, nested: { yes: 1 }, array: [{}, { yes: true }, {}] });
+    });
 
   });   // ==== End of 'Deep copying' ==== //