Making the application run as trial version

Question

Hi, I need some help from u experts... I have a Windows Application..that i would like to deploy as a trail version making the application run bet two specific Dates(i.e for 3months)...i need this application to be in such a way that the source code should never be traced by others...so where should write the code so that its hidden and cant be changed(like metadata) in future. Plz help as im in need of it very soon... Thanks in Advance.