I think yuo should plan your SQL Server installation in such way that log shrink is never needed (ok in some extreme cases - yes)
So - if your database is in Full recovery mode do a full backup and log backup. This will allow you to shrink log by using DBCC SHRINKFILE command
Kindest Regards,
Damian Widera
SQL Server MVP,
MCT, MCSE Data Platform, MCSD.NET