Whats wrong?!?

PHP:

$random = array_rand($this->getOwner()->battle1, 2); 
unset($this->battle2[$random[0]]);
unset($this->battle2[$random[1]]);
$this->getOwner()->zombie2 = $random[0];
$this->getOwner()->zombie2 = $random[1];

Why does that not work?
PS: Its in a task and the array works and so

Array_rand method does not return an array, it returns a random key from an array.
http://php.net/manual/en/function.array-rand.php

Okay and how can I fix it?

PHP:

$random = $this->getOwner()->battle1[array_rand($this->getOwner()->battle1, 2)];