Forcing User to Use LOV

[JJOHNS]

I have a form with a field that has a list of values associated with it. It's not actually set up as an LOV. Rather the original developer created a List Canvas that works like an LOV. Right now the user can key in the data in that field and get the rest of the record, but I want to force the user to select from the list. I don't want him to be able to key in data in that field.

Can someone suggest a way to do this?

Thanks,