Max Trail Length option helps you to set the maximum Audit Trail length you want to keep. 

When the number is set, any audit trail entries will be automatically removed when the given limit is exceeded.

Default: 1000

Note: Max Trail Length is a premium feature and only available to Pro subscribers. To find out what the extra features for Shield Pro are, read the article here.

Free users will be limited to 100 events, Pro subscribers will be unlimited.