Generally getting rid of mice from your home is a straightforward process. The treatment usually takes a few visits until I can give you the all clear. However, preventing more mice from entering at a later date is not always so simple.
The type of building is the main factor when considering preventing future access. For example a newer detached property would be the easiest to proof, and a terrace property would be the most difficult. Let me explain the reasons for this. Mice Generally enter homes at ground level, air vents, weep holes and gaps around pipes and the most common entry points.
In a detached property all these points are easy to access. I can walk around your property and very quickly point out the areas that need attention.
In a semi detached property you will need cooperation from your neighbour, as even if you follow proofing advice on your home mice can find their way in from next door. through wall cavities, in between the floors etc. To a mouse its one building, if they are in one side chances are they will be in the other side as well.
Unfortunately, preventing access in a terrace is next to impossible as everyone in the terrace will need to fill gaps and fit air vent covers and getting everyone's cooperation is unlikely. If this is the case don't panic there are still a few things you can do, it won't be as effective as proofing externally but will help.
Look for holes around pipes internally. Look for these under kitchen units, store cupboards behind bath panels etc..fill these gaps with wire wool to reduce the chances of mice travelling between properties.