Limiting character length of custom field

Hi,
I’ve been working on this for a while now with no success, so I thought I’d put it up the forum.
I’ve tried using a few php methods I found online but, while they work, I can only place my custom field “somewhere in the loop” with them, so the field doesn’t display within my search results custom fields layout.
I was wondering if anyone could suggest a way to either:
Limit the amount of characters imputed within a custom field box on the add listing page,
Or
Simply not display the additional text (if any) on the search results page for that custom field.
I’d be grateful for any advice.
Paul