Seems like a table of goals would make sense as you can then use relationships, a sort order or a filter to access the most recent goal.
Do you have any example files or detailed description. It's hard to start from scratch.
I'm just looking at this from a general perspective. It's not all that different than, for example, the Version History portal found on the opening layout of the Known Bugs List.
If your portal records auto-enter a serial number, you can specify a sorted portal or sorted relationship that sorts on that serial number field in Descending order to make the most recently created goal record either the one goal visible in a field on your dashboard layout added from the related table (if relationship is sorted) or from a one row portal (if the portal is sorted).
You might also sort on a date or timestamp field to get essentially the same result.