contractors on my property with out notice

I have contractors that keep coming to my door on days I am not home.  My dogs have access to the outside yard.  The last time they came, they rang doorbell and went into my back yard.  Luckily my son was home.  They are showing up without notice and I have asked them through my doorbell to come back on specific days when I am working from home.  Yesterday i left work to try to find the contractors to tell them to come back.  I just need to lock dogs up.  But no such luck, the guys in area said that crew left.  And the other crew did not speak English.  I need to contact someone because I have read horror stories of contractors being bite by dogs, dogs got out or the dogs were taken to a shelter so work can be done.  I don't want any of this to happen, so I need to schedule a time for them to come out and not just randomly show up.  I work in an office 40 min away.  Who do I contact to get this done?