Try a few varieties of perrenial clovers that are recommneded for your area. There are selective herbicides that can be used to control unwanted grasses and broad leaf "weeds". You can use a 40% Glysophate product, but only in a light doseage up to 1% max. But why run the risk of wiping out the clover when the selective hebicides work great, are simple to apply and are not all that expensive.