A plant is particularly subject to danger at the end of winter and whenever the new growth is tender.
In general, deer will not jump over anything they can’t see over.
 

In landscaping the yard, it is wise to remember that deer ritually follow certain pathways everyday.  It is wise to put the more tempting plants away from these pathways.  In some yards deer will not cross hard surfaces such as walks and driveways.  Sometimes it is even possible to design a portion of the landscape comprised of tall plants that deer generally avoid.  This can create kind of a hallway that deer can use as they cross through your yard.  It is not easy to accomplish, but it is sometimes possible.
 

There are all kinds of “repellents” (human hair, bars of soap and playing radios) that people find to keep deer away from their plants.  Deer quickly adjust to all of these “repellents”, and no single one seems to be reliable for more than a few weeks.  Change is the key for these supposed repellents to work at all.   I find the best repellent to be a monthly application of Milorganite fertilizer.  Milorganite is made from the sewer sludge from the city of Milwaukee, where there are several major beer breweries.  Rumor has it that Milorganite has a slight essence of both beer and humans, which the deer associate with hunters.  Whatever the case, it does seem to work - at least over the growing season months.  Sprays, although they have to be re-applied every few weeks (depending on the rain), are effective for short periods.  Ropel and Tree Guard have worked the best for us.  Securely netting the shrubs, especially in the winter, with almost-invisible black plastic netting can work effectively.  Evidently, deer wish to avoid the sensation of their teeth getting tangled in the netting.  Repellex tablets, though expensive, are an excellent long term repellent. 
 

To confuse things even more, deer have regional taste preferences.  What they will eat in one neighborhood they will avoid in another.  Some plants which are particularly subject to regional taste preferences are:  white pine, holly (except American holly), aucuba, deciduous magnolias, cornus mas, camellias, nandina, Japanese maples and birds nest spruce. 
 

A species that deer will browse as a newly planted small plant will often be left untouched as a mature, established plant.