You can buy plastic spiky strips that stop them landing on window sills etc, which could be placed along the top of a roofed bird table.
I stopped putting feed straight on to flat surfaces such as tables and lawns and now use metal/plastic feeders and I added a roof to my bird table, both of which large birds have difficulty with. The net bag can trap the legs of small birds so I do not use them.

Three sides of my bird table have been panelled over, and I have drilled 2 x two inch holes in each panel which allows all the small birds onto the table. The fourth side I have used half inch wire netting covering all except the bottom two inches. Fold the netting at thebottom so the small birds dont hurt themselves . This has cured the pigeons emptying our table and we see very lttle of them.

I use the long bird feeders that hang, the bluetits especially won't eat the corn in bird food and can be seen picking it out and dropping it on to the soil.....we had quite a crop one year.....so a shallow saucer was fixed to the base of the feeder this fills with corn that only the collared doves eat so everyones happy

thanks everybody, you gave me some ideas on what my neighbor and i can do to solve our problem!!