A family of Microsoft relational database management systems designed for ease of use.
Lets leave off the New dog name for the moment. It adds a level of complexity you don't need right now.
The Rowsource you show doesn't include the customer name. Lets go back to here:
RowSource: SELECT CustomersT.[Customer ID], DogsT.Dogs Name], Lastname & ", " & Firstname AS CustName
FROM CustomersT INNER JOIN DogsT ON CustomersT.[Customer ID] = DogsT.[Customer IDFK];
ORDER BY [Dogs Name];
Bound Column: 1
Column Count: 3
Column Widths: 0";1.5";2"
Nothing is going to happen when you select a row in the combobox because you didn't do the last part.
From my previous note:
In the After Update event of this combo I would use code like:
Me.Filter = "[Customer ID] = " & Me.cboSelectDog
DoCmd.runCommand acCMDApplyfilterSort
By the way its not a good idea to use spaces in object names. This will come back to haunt you.