How to random array?

[achoo254]

2 all,

I'm don't know how to display random array in strings. Example:

$display = 'hello word - hello word - hello word';
$find = ('h'); 
$replace = ('.$my_array .');
$my_array = ('1','2','3','4');

when code display:

h1ello word - h1ello word - h1ello word

Re-load page:

h2ello word - h2ello word - h2ello word

So, how to display like this:

h1ello word - h2ello word - h3ello word

Please help me, thanks