Spawn protection

-- Obviously change these to your area
local startpos=Vector(0, 0, 0)
local endpos=Vector(1, 1, 1)
local interval=0.2 -- You should probably leave this above 0 because I don't know how taxing ents.FindInBox is, but play with it.  If 0 works, put it to 0, as that'll be the best thing you can do

local nextThink=0
hook.Add("Think", "removeSpawnAreaorWhatever", function()
    if (CurTime()>nextThink) then
        for f,v in pairs(ents.FindInBox(startpos, endpos)) do
            if v:GetClass()=="prop_physics" then
                --Do whatever you want to run before removal here, obviously
                v:Remove()
            end
        end
        nextThink=CurTime()+0.2
    end
end)