Unique array_rand once per page

I have a variable composed of 4 values : $valeur_aleatoire = Array('word','word2','word3','word4');

Random values are generated in this way :

Blabla bla bla blablablabla . Bla bla blablabla bla bla bla blablabla.

This content is inserted in the page single_post.php, and is used on every post. I want the values to be generated only once per page in order to fix the content on each page. Currently, the content changes every refresh.