Dynamic Row Level Security on intersection of 2 fields from different tables

I have a requirement for dynamic security that I haven't been able to figure out.  Not sure if it's a tool limitation or just requires more complicated DAX than I understand.

The requirement is to secure on a combination of Country and Business Unit.   These are both attributes/master data fields.  So I have a fact table, and then 2 dimension tables.  (1 dimension table contains Country, 1 contains BU)

Below is an example from the Security table

When I try to add the DAX filter logic, I have to pick 1 of the dimension tables to apply the filter, and if I try to reference the column from the 2nd dimension table, I get an error during the syntax check.

"The column 'table2[Country]' either doesn't exist or doesn't have a relationship to any table available in the current context."

I was able to get this to work in a POC I did but both Country and Business Unit were on the same table in that example.