backup as compressed backupset database  plus archivelog;
delete noprompt obsolete;

 backup archivelog all; 

 
 configure controlfile autobackup on;
 configure backup optimization on;
 configure retention policy to redundancy 5;
 configure archivelog deletion policy to  backed up 1 times to DISK;
 configure retention policy to recovery window of 7 days;

The big thing here is what was the *cause* of a missing archive log?

Was it disk failure? If so, they should be mirrored
Was it human error? If so, then that process should be corrected
If it was a complete server/site failure, then perhaps DataGuard should be explored so you have a near real-time copy of your data.

Backing them up more frequently or having more copies of them is worth pursuing as long as you can justify the reasons why you need to do so. Because (for example) if archives go missing because of human error (either directly or indirectly via say a cleanup script) then really I'd be tackling that first.

In my experience, people fall into a few broad categories

a) they don't want lose their database no matter what, so they have DataGuard to ensure that everything (including archive logs) is being sent to an alternate location (where that might be an entirely different site, or a different data centre, or even just a different server).

b) they're confident in their infrastructure that they wont lose archivelogs unless a major incident occurs, so they back them up perhaps once per day

c) a hybrid where DataGuard is not in use, so they ship their archivelogs manually to an alternate destination (either via RMAN backups or home grown scripts).

Hope this helps