|Deer park at Kentchurch Court, UK|
Deer parks were often constructed with a bank topped with a pale, or fence. Inside the bank was a ditch, unenticing to deer. Rather than "corral" the deer, large parks were built in already forested areas where deer were likely to be, and deer leaps were constructed. A deer leap was a gentle ramp that led from outside the park over the bank and down a narrower ramp to the park. The ditch in that area would be much deeper, and the likelihood of deer wandering out again was slim.
The area inside was landscaped to make it suitable for deer and yet still attractive to garden-loving people. Trees were trimmed to make the deer more visible, and yet still give them a place to flee so that the hunt was not boring. Parks could be many miles in circumference—Woodstock, north of Oxford, was seven miles around—or small enough to be visible all at once.
Not all parks were for the use of the king. Other nobles with sufficient land could establish them, but only after being granted a royal license "to empark." This might be done less for sport than for ensuring a steady supply of venison. Because of the number of parks, deer could usually be hunted only by the nobility. Venison, therefore, became essentially a dish for the table of nobility, not a meat one could find at market.
Deer parks took effort to maintain, however, and this probably led to their demise. Henry III's bailiff, for instance, in 1251 had "to remove the bodies of dead beasts and swine which are rotting in the park"—a time-consuming task, given the area to be covered in the several deer parks owned by the king. There was also the trimming of trees to be done, and maintaining the pale. The fact that the deer were hemmed in sometimes led to starvation, especially in winter when they could not range for food. Few deer parks exist today, unless they have been revived by an interest in history.
...or ecology: at least one scholar sees value in studying deer parks now, saying
Where deer parks survive, and even this is rare, they do so as a unique landscape separated in time and function from their origins. They reflect the landscapes of the time and place they were emparked and the changes in economic function and ecology over a long lifespan. ["The Ecology and Economics of Medieval Deer Parks," Ian D. Rotherham, Landscape Archaeology and Ecology, 2007]