Лучше это как-то так сделать:
+    private int layerCount = 0;
+
+    private static final int LAYER_BACKGROUND = layerCount++;
+    private static final int LAYER_FIRST_WAVE = layerCount++;
+    private static final int LAYER_SECOND_WAVE = layerCount++;
+    private static final int LAYER_THIRD_WAVE = layerCount++;
+    private static final int LAYER_PERISCOPE = layerCount++;