Synchronized thread safe Dictionary

While working in a multi threaded environment i tried to work with a dictionary today. After reading some documentation on msdn i understood that the Dictionary class is not really a thread safe class and if we want to do that we need to make it thread safe we need to do it ourselves.
I understood the fact and tried to write a wrapper over this class and make a generic thread safe dictionary for using it in my application.
So what i did in this wrapper is i maintained a reference to the generic dictionary and implemented IDictionary interface. I plainly delegated the calls to the reference however made sure that each of the call acquires the lock over the object and hence i assumed that my dictionary is a thread safe dictionary.
However while discussing it with one of the colleagues i realize that still is not really a thread safe class. It can still cause problem when i am trying to use IEnumerator. Let's see how

when we loop through a dict with 3 elements with SynchronizedDictionary

foreach(KeyValue keyValue in dict) {...}

will perform like

lock

get enumerator

unlock

<--- another thread might modify as dict is not locked now

lock (assuming returned enumerator calls this[TKey key] for fetching items. else it won't be even locked!)

get first item

unlock

<--- another thread might modify as dict is not locked now

lock

get second item

unlock

<--- another thread might modify as dict is not locked now

lock

get third item

unlock

and hence there's a problem.
Any suggestions out there so resolve this problem.

~Abhishek