You can spawn static missions over land or on water.
This can be done by laying out everything for your static mission in the editor, 
then exporting the data from your mission using a simple script and a copy - paste - edit strategy.

My approach to doing this as follows:

1) Start the Eden Editor.
2) Lay out your static mission. You should:
	[Optional] place a marker indicating where it will spawn (save your work)
	Place all buldings, sandbags, etc (save your work)
	Place any vehicle, navel, sub or air patrols - note that they will patrol using the postion at which you place them as the centerpoint of their patrol.
	(save your work).
	Place any static weapons. These can be outside, on top of or inside buildings.
	(save your work).
	Place a unit at each location you wish to have a group patrol OUTSIDE buildings. These will spawn as infantry on land and scuba units over water.
	Place a unit inside buildings as appropriate.
	Place some sort of ammo box, cardboard box, or other loot container if you wish to have one. You can have as many as you like. 
	Save your work.

	**  NOTES  **
	Uniforms, weapons and any other customization to units will not be preserved.
	The defaults for blckeagls, or any specific definitions for _uniforms, _weapons, etc provided when the mission is spawned, will be used for these AI properties.
		
3) Export the mission data using the tools provided.
	In the EDEN editor, go to tools\debug console
	in the box type execVM "pullStaticMission.sqf";
	Click 'local exec'
	Hit Esc and wait for the script to run. You will see a notification in the lower left corner when it is done.
	Alt-Tab out and past the output into your text editor.
	Make a copy of the stati mission template.
	Copy relevant information from the text you just grabbed with the clipboard to the template.
	Make any edits or other adjustments needed.

	Once you have done this, add the file to the custom_server\Missions\Static\missions directory then
	add an entry for your static mission to GMS_StaticMissionLists.sqf