Two other options, that are not in-game:
* Reduce the spawn rate in the Tinkers Construct config (I think, it was 8 originally. Take it down to 2 or 3)
* Update the Unleashed pack or at least Tinkers Construct. Later versions get rid of the spawns and introduce the floating islands instead. (Again, take the spawn rate down or they spawn way too often.) And when you get some saplings for the trees on the islands, then you don't need any slime spawn at all anymore. Just farming the trees will get you enough green and blue slime balls.
The in-game solution for me was to use Natura's berry bushes as fences. They grow 3 high, no slime was able to get through there.