Reposition sprite nodes after SKAction is completed - ios7

Question

I am trying to reposition my sprites after an SKAction moveTo action is completed. I have programmed the enemies to enter the screen from (self.frame.size.width/2, 0). They are moving only on the y axis. I want to reposition them on the initial position when their y position is bigger than (self.frame.size.height) and move them again and again in the same way until the player kills all of the enemies. I am struggling on this point.What part of code should I add? Any ideas? This code might help you understand my implementation :
-(void) addEnemies {
for (int j = 0; j < 6; j++) {
SKSpriteNode* enemy = [SKSpriteNode spriteNodeWithImageNamed:#"player"];
enemy.position = CGPointMake(((self.frame.size.width) -20) - j * (enemy.frame.size.width) , 0);
CGPoint realDest = CGPointMake((enemy.position.x), (self.frame.size.height));
float velocity = 50/1.0;
float realMoveDuration = self.size.height / velocity;
SKAction * actionMove = [SKAction moveTo:realDest duration:realMoveDuration];
[enemy runAction:actionMove];
[self addChild:enemy];
}
}

Answer 1

-(void)addEnemies{
for (int j = 0; j < 6; j++) {
SKSpriteNode* enemy = [SKSpriteNode spriteNodeWithImageNamed:#"player"];
enemy.position = CGPointMake(((self.frame.size.width) -20) - j * (enemy.frame.size.width) , 0);
[self addChild:enemy];
[self moveEnemyNode:enemy];
}
}
-(void)moveEnemyNode:(SKSpriteNode *)enemy{
enemy.position = CGPointMake(enemy.position.x, 0);
float velocity = 50/1.0;
float realMoveDuration = self.size.height / velocity;
SKAction *actionMove = [SKAction moveToY:self.frame.size.height + enemy.frame.size.height duration:realMoveDuration];
[self runAction:actionMove completion:^{
[self moveEnemyNode:enemy];
}];
}

Answer 2

Create a SKSpriteNode that replicates a roof -> Rectangle(self.frame.size.width,1)
Have it sit along the top edge of the screen with a non-dynamic physics body
Set the "roof" and enemy to contact each other
Call a method on contact that resets there position and calls the SKaction
This allows you to have direct access to each enemy exactly when it hits the top of the screen.
Here is an example of how to create a roof and have enemies interact with it. https://stackoverflow.com/a/24195006/2494064