Thread: Window guards?

Hiya
have not posted in a while but ronnie and reggie are doing really well we have just built a 8ft by 4ft by 6ft high cat run for them to safely enjoy some fresh air when we are in garden
question now is for those of you that have there maines as house cats like me how do you tackle the windows bein open???
with summer coming up obviously we need windows open but i dont want the boys getting out either do you put anything on your windows if so what and were can i buy
thx