I have a full wall slide and have the same issue. 36' RV with about a 32' slide, it came with these:
http://www.dyersonline.com/alta-adjustable-slide-lock-room-security-system-13-23.html?utm_medium=shoppingengine&utm_source=googlebase&gclid=CjwKCAiAz7TfBRAKEiwAz8fKOFwDCea7bFBQ1itmX1Su7rvVlTQl11Vfcxdv3fB99MJ-rHkKvOWOhRoCLZgQAvD_BwE
They are in my owners manual and how to install them. I would install them lower then the picture shows, about 1/3 way down from the top. These will stop slide creep while traveling or in storage.
CAUTION: have some way to ensure that they are removed prior to trying to put out the slide. I put blue painters tape over the slide switch. Similar to hanging your RV keys from the crank handle for the OTA TV antenna. Little reminders.