The biggest thing to note when using the conduit as a casing for an underground fence is that the conduit does protect the wire.
If something were to happen to the wire and it became damaged in any way, the conduit makes it much more difficult to get to the wire.
If you foresee any types of issues that would allow for quicker breakdown for your underground fence, should steer clear of conduit wherever possible for easy repairs.
There is, of course, the option to use conduit in some areas, and not others, to make potential repairs easier.
You also have to be careful if you are choosing to use an existing conduit to run your fence through.
There is always a risk that the wires inside could interfere with each other, causing damage to your underground fence, or other utilities running through the wire.
Another important consideration is the ease of laying the underground fence in the first place.
In many cases, it may be easier to set up the wire without using a conduit, especially when running it along sidewalks or driveways with existing cracks.