University of Maryland Extension

How do I keep out deer?

UMD Extension has an excellent guide to "Managing Deer Damage in Maryland," by Jonathan Kays. It includes a particularly helpful section on different fence designs. If possible, build your deer exclusion system BEFORE planting. Once deer know that something delicious is behind a fence, they become much more determined to get past that fence.

When building fencing, also take local zoning rules into account.
Baltimore City's zoning and building codes are online here:  
The section on fencing rules is in this document called "BUILDING, FIRE, AND RELATED CODES," under "SECTION 3114 FENCES," on page 103 (p. 129 of the file).
For other urban parts of Maryland, here are links to your local zoning authority: 

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