Having worked for Terminix in pest control in the past, I would have to say there is no "foolproof" way to keep them
all out.
However, if one is bothered by an unusual number of them or allergic to them, something you can do by yourself is to get the sticky glue traps (which you can get at most hardware stores, Agway, etc.) and place them along the walls in places where you, your stuff and your animals won't accidentally get stuck to them. They will catch many bugs, including spiders.
To further keep insects from entering the domicile, the best solution is to have a professional pest service (
) spray the outside and inside with an insecticide which will leave a residue. All professional pest services have solutions which will
not have an effect on humans or animals but will kill bugs.
You can buy insecticide sprays commercially, but they have to be manufactured to be less effective because you don't need a state-issued license to apply them. Most of them do not leave a residue and are merely contact killers, meaning you have to "hit" the insect with them.
Try the glue traps first and, if they don't get enough of the critters, have your place sprayed professionally.
This is my opinion only, but is based on years of experience.
Good luck with your problem.
Larry