put a timer control into form. and add a property for save time into form. adjuct timer for 1 seconds. and put these lines into resize event:

thisform.savetime=seco()
thisform.lockscreen=.t.


and put these lines into timer control:

if seco()-thisform.savetime<1
retu
endif
thisform.lockscreen=.f.

note:
i have not tried this method. this is only hypothesis. :)