guard systems SHOULD be travelled by enemies sometimes. - so - don t make flying in them impossible as you don t achive anything by that. - guard systems are often sort of "outside" the vanilla RP, with much larger bases, rediculously strong defenses etc.
but if you simply "don t like visitors" at all - you could simply put 6 platforms to the jumphole with quickfiring admin cannons - then you ll sit in your nice guard system, all alone... .lonely forever, cause no one ever even tries an incursion - and wheres the point in that.