Assets expensed for tax purposes --How to do it?

Hello,

How do I set up a Depreciation Method so that the asset will fully depreciate in the current fiscal year? We have assets that need to be 'expensed' on tax books, and depreciate out for the life of the asset on the financial book.
I created a new depreciation method in AM02.2 using the percentage tab with Year 1 = 100 -- however if the asset is placed in service, for example, in Per 4 - I want it to still be fully depreciated (on tax books only) after running depreciation in Per 12.

Is there something I am missing ? Any ideas on how to fully depreciate the asset on tax books fully in the current fiscal year??

Much thanks !