diff --git a/deckhand/engine/document_validation.py b/deckhand/engine/document_validation.py
index a4247da1..c874766c 100644
--- a/deckhand/engine/document_validation.py
+++ b/deckhand/engine/document_validation.py
@@ -78,6 +78,8 @@ class BaseValidator(object):
     validation.
     """
 
+    __slots__ = ('_schema_map')
+
     _supported_versions = ('v1',)
     _schema_re = re.compile(r'^[a-zA-Z]+\/[a-zA-Z]+\/v\d+$')
 
@@ -103,6 +105,8 @@ class GenericValidator(BaseValidator):
     or abstract, or what version its schema is.
     """
 
+    __slots__ = ('base_schema')
+
     def __init__(self):
         super(GenericValidator, self).__init__()
         self.base_schema = self._schema_map['v1']['deckhand/Base']
@@ -153,6 +157,8 @@ class GenericValidator(BaseValidator):
 class DataSchemaValidator(GenericValidator):
     """Validator for validating ``DataSchema`` documents."""
 
+    __slots__ = ('_default_schema_map', '_external_data_schemas')
+
     def _build_schema_map(self, data_schemas):
         schema_map = copy.deepcopy(self._default_schema_map)
 
diff --git a/deckhand/engine/layering.py b/deckhand/engine/layering.py
index e3da005d..fed632fb 100644
--- a/deckhand/engine/layering.py
+++ b/deckhand/engine/layering.py
@@ -47,6 +47,10 @@ class DocumentLayering(object):
         together into a fully rendered document.
     """
 
+    __slots__ = ('_documents_by_index', '_documents_by_labels',
+                 '_documents_by_layer', '_layer_order', '_layering_policy',
+                 '_parents', '_sorted_documents', 'secrets_substitution')
+
     _SUPPORTED_METHODS = (_MERGE_ACTION, _REPLACE_ACTION, _DELETE_ACTION) = (
         'merge', 'replace', 'delete')
 
@@ -149,7 +153,6 @@ class DocumentLayering(object):
         # Mapping of (doc.name, doc.metadata.name) => children, where children
         # are the documents whose `parentSelector` references the doc.
         self._parents = {}
-        self._parentless_documents = []
 
         for layer in self._layer_order:
             documents_in_layer = self._documents_by_layer.get(layer, [])
@@ -179,7 +182,6 @@ class DocumentLayering(object):
                         'Could not find parent for document with name=%s, '
                         'schema=%s, layer=%s, parentSelector=%s.', doc.name,
                         doc.schema, doc.layer, doc.parent_selector)
-                self._parentless_documents.append(doc)
             # If the document is a child document of more than 1 parent, then
             # the document has too many parents, which is a validation error.
             elif all_children[doc] > 1:
@@ -356,9 +358,9 @@ class DocumentLayering(object):
 
         self._layer_order = self._get_layering_order(self._layering_policy)
         self._calc_all_document_children()
-        self._substitution_sources = substitution_sources or []
+
         self.secrets_substitution = secrets_manager.SecretsSubstitution(
-            self._substitution_sources,
+            substitution_sources or [],
             fail_on_missing_sub_src=fail_on_missing_sub_src)
 
         self._sorted_documents = self._topologically_sort_documents(documents)
@@ -499,3 +501,7 @@ class DocumentLayering(object):
 
         # Return only concrete documents.
         return [d for d in self._sorted_documents if d.is_abstract is False]
+
+    @property
+    def documents(self):
+        return self._sorted_documents
diff --git a/deckhand/engine/secrets_manager.py b/deckhand/engine/secrets_manager.py
index 3beb5042..f1dd2b02 100644
--- a/deckhand/engine/secrets_manager.py
+++ b/deckhand/engine/secrets_manager.py
@@ -114,6 +114,8 @@ class SecretsManager(object):
 class SecretsSubstitution(object):
     """Class for document substitution logic for YAML files."""
 
+    __slots__ = ('_fail_on_missing_sub_src', '_substitution_sources')
+
     @staticmethod
     def sanitize_potential_secrets(error, document):
         """Sanitize all secret data that may have been substituted into the