I use reolink camera's and nvr set up.
but you can use the cameras as stand alone and pull it up on computer or an app.
they also have internal slots for sd cards to record for a while.
you can set them up for notification as well.
while they do have battery powered wifi camera's that would work for your fence application, if it is visible from the front door, why not mount a camera pointed that way instead?
I have one of the battery powered ones, but didn't like having to replace the batteries. depending on traffic in the area they last about a month for low traffic. a week with high traffic. just had a bunch of rechargables to replace them with.