Android Question Manage Lock Object

You do not need to use a Lock. What exactly do you want to block?

In My activity i manage :

MarkersFocusOverlay1.RemoveMarkers()
MarkersFocusOverlay1.AddMarkers(Markers)

in :

LocationMobile_LocationChanged(...)
and
GeoPoi_GeocodeDone(Results() As Address, Tag As Object)

not a problem?

No. Your code runs in the main thread.