I'm trying to recreate a map from Warcraft 2 in Starcraft 2 and to keep the same game play flow is impossible. Changing all air units to be ground pathing gets it close, but not 100% because of the lack of water-specific pathing. In Warcraft 2, the 2 players had an island all to themselves and shoreline prevented the AI from doing land drops except via a specified sea port, and the occasional air unit flying over to say hi.
The reason I need fly pathing blockers is because there are a lot more air units in Starcraft 2 than Warcraft 2, whereas the overwhelming majority of units in Warcraft 2 were land units. A decent Starcraft 2 army can be entirely composed of air units and do much more damage than an air army in Warcraft 2 (and the War2 AI wasn't smart enough to make an army of all air units). In addition, Warcraft 2 had no air-based transport units, forcing the AI to do sea-based drops at your port. This allowed the players sufficient defense planning as they gathered their forces to assault the AI's islands.
In Starcraft 2, this means blocking air unit pathing around the players' island except via the port to prevent the ridiculous drops the AI does at the most vulnerable sections of your island. The map is ridiculously hard without this limitation in the Warcraft 2 version.
The best I can get is to have air units "walk" and create shore all around the AI's islands and connect it to the players' island by a small channel. This means you can sort of attack in places that were impossible in the Warcraft 2 version without massively changing the terrain around the players' island.