SQL Job for Monitoring Blockings on SQL Server
One way to do this is to set Blocked Process Report to 60 seconds, then an event will be raised by SQL.  This event can be picked up in a number of ways.

1) Via SQL Profiler, this isnt a great way as you have to run trace etc to find them

2) Via Extended Events, again not great you would have to have a job constantly polling the target.

3) Via Event Notifications.  This is a great way and I think the best way of doing it.  You can create an Event Notification and a Service to direct the notification into a Service Broker queue, then you can process the queue messages with a stored procedure.  It is a fantastic way of getting a free monitoring tool for yourself.

http://i.zdnet.com/whitepapers/Quest_How_to_Use_SQL_Server_Extended_Events_and_Notifications_to_Proactively_Resolve_Performance_Issues.pdf

Just follow page 24, but change the event from ERRLOG to BLOCKED_PROCESS_REPORT

By Default blocked process report is set to 0 (disabled) so to enable you will have to:

SP_CONFIGURE'blocked process threshold',60;
GO
RECONFIGURE;
GO