Robust ways for checking allowed values in a column

 select form from mytable  where form ~ '^Canal$|^Drain$|^Foreshore$|^inlandRiver$|^Lake$|^lockOrFlightOfLocks$|^Marsh$|^Researvoir$|^Sea$|^tidalRiver$|^Transfer$'

I used ^ and $ to ensure checking of allowed values.

However, 'Backyard' was selected.

Why is that?

Regards,

David