1. Create a Dynamic Constituent Query for all deceased constituents
  2. Click Config > Business Rules
  3. Under User defined rules, click Constituent
  4. Click New Opening Constituent Rule
  5. Add the Rule Name, Query (from step 1) and Message
  6. Add security by group if desired
  7. Mark Gifts and/or Actions if you want the rule to trigger if one of those records is opened directly
  8. Click OK