destroy directive watchers

var unwatch = scope.$watch(function() {
				return ngModel.$modelValue;
			}, function(newValue) {
				if (newValue && (newValue.charAt(0) == '&' || newValue.charAt(0) == '?')) {
					//scope[attrs.ngModel] = newValue.slice(1);
				}
			});
			ngModel.$modelValue = newVal;

			scope.$on('$destroy', function() {
				unwatch();
			});