Yes its a good spell, interacts with corrode, and contrasts with sacred ground. Those are covered in other rules-based threads.
Just now I wished this were a conjuration rather than an enchantment. It would interact better with Harshforge monolith, construction yard, dispel, goblin builder, and presumably other stuff im not thinking about.
Interacts worse with zone attacks, force hammer, and creatures with nothing better to do than attack.
Fortifications seem more like conjuration territory. Who should be better at fortifying a position? a goblin builder or a pixie named fellella?
The only enchantment worth dispelling in my warlord books half the time is fortified position. I'd rather those dispels sit wasted in my opponent's spellbook.