I'm also wanting to make it continue under that part count, but I just don't know how. Please help!
local Region = game.workspace.Region
local Rep = game:GetService("ReplicatedStorage")
local Mine = game.ReplicatedStorage.LandMine
local x = Region.Position.x
local z = Region.Position.Z
local xS = Region.Size.X/2
local xZ = Region.Size.Z/2
while true do
local newmine = Mine:Clone()
newmine.Parent = workspace
local pos1 = math.random(x-xS,x+xS)
local pos2 = math.random(z-xZ,z+xZ)
newmine.Position = Vector3.new(pos1,0.2,pos2)
wait(1)
end

3 comments
so like.. if parts > num then break end..?
Make a folder for the LandMines,
Make a folder for the Land Mines, this depends whether your landmines are models: local i = 0 for _,v in pairs(workspace:GetDescendants()) do if v:IsA('BasePart') then -- change BasePart to Model if the landmines r models. i = i + 1 end end print(i)