Wireless or wired solution for perimeter fence security?
To be clear I don't understand wireless the ways the engineers here do, and that may be the best option for you.  When you're evaluating wireless though, take into account battery cost, effect of temperature on battery life if you have high or low temperatures there and impact on the old envirothingy.  Bear in mind wireless communication and wired power is an option.  If you really think you can get a battery to run for a year or two, great, But if the fence is for security purposes, as people have suggested in the comments, nuisance tripping could cause your system to be active much more than you think.  Also keep in mind that all I know about your building is that it is a university and 1 km sq, and most of this advice relates to a permanent hardwired system, so many concerns like whether to run underground or surface mount will largely depend on the existing quality of finish of your buildings. 

Think about the interface you'll make available to your security office as well.  If the fence is chain link, One person hopping the fence will likely cause 3-5 sensors to detect vibration.  A quickly scrolling text window full of verbose alarms is functional but irritating.  If you can provide an interface that shows the perimeter as a ring and changes color in proportion to the strength of the vibration, your guards will instantly know where they need to check with just a quick look.  Small vibrations from wind gusts would show up as a slight change across the whole diagram and would be easy to disregard.  This sort of more active setup would be a main advantage to hard wiring.


  We are currently working on a project where we would like to place around 350 vibration sensors on our university's perimeter fence for security. The field layout is almost 1km to 1km (square - 1km^2 - 4km of fence).


Very nice.  Depending on the desired quality of finish, if you go with a wired option, you'll likely need to run undergrounds and 90 up out of the dirt for each sensor, or run some manner of armored cable along or through the fence.  Use stranded wire.  Make sure you take expansion into account.  Your sensors are 1 every ~11 meters, so for underground conduit the 90s up will provide adequate expansion, but if you were to run things in armored cable and do so "tightly" between devices in an attempt to make it look neat, contraction from temperature change could do a lot of damage.  Ensure the system has adequate expansion joints.  If you decide to run flexible or other conduit along the fence itself, figure out what your mechanical failure points are, because if something destroys a section of fence, like a car driving through it, horizontal runs of conduit with no suitable failure points could tear off and damage sensors a significant distance down the fence, and the ripping sort of damage that kind of thing does is likely to be time consuming to repair.  Crossing existing perimiter roadways and sidewalks can be another concern requiring ingenuity or money.  The advantages of hard wiring only matter if you make use of them.  Consider future security devices that you might want anywhere on the perimeter and consider whether they should run off the same power bus if they're low power.  If you're going to be adding cameras on each corner two years from now and you're digging a trench for this project, get the other pipes you'll want later in the ground and make sure you can locate the ends again later when that other project goes forward.

If you do a good job of hardwiring it, you can expect little or no maintenance and the cost of batteries could offset the cost considerably, so that's nice.  Use stranded wire if possible and size the wire so that all devices can be powered from either end of the loop.  

You can also make a hardwired setup quite tamper resistant by using a loop design where you feed both ends of the loop.  The power wires can be protected with ground fault warning and each device can detect and block downstream overcurrent.  If someone cuts the loop at any location, you will read ex. Sensors 1-138 from one loop end and sensors 139-400 from the other and you know exactly where the tamper has occurred.  Downstream overcurrent protection will prevent resulting shorts from affecting the other sensors.