DB2 .NET Query Syntax

Hi,
I am trying to use similar to:

where IPROD LIKE '%' + @IPROD +'%'
I am using DB2 and it does not like '+' and @Fieldname (e.g. @IPROD where it is a key in search field)

SQL0402: + use not valid.
It does not work with (@IPROD), thus I use '?' which works fine.

I tried below in combination and does not work either.

SELECT ID, IPROD, DESC, TYPE FROM CARMODEL.MA01 WHERE (IPROD LIKE '%' || ? || '%')

Any Help is appreciated!