app to make wifi stay on certain wifis

[piff]

why does the android always try to connect to other known wifi spots? for example, I am connected to my linksis at home that has a password but there is another linksys thats open. The android keeps going back and for with each one, I guess because of signal fluctuations.is there any wifi app that lets you set a priority to wifi networks? because I dont want to forget the open linsys network because i might use it out in the street somewhere