Dependable query to determine who is connected to a database

I want to programmatically restore a database from backup.  But in order to do so, one must first break all existing connections to that database.  The following queries list NEARLY all connections:

select spid, rtrim(loginame) from sys.sysprocesses where db_name(dbid)='MyDatabaseName'
sp_who
sp_who2

Unfortunately, those queries do not always list every last connection.  Once in a while, those queries miss a connection.  After running one of the above queries, it is easy enough to kill all reported user connections.  Unfortunately, this process does not always report and kill every connection.  I need a query to show every last connection to a database so that I can kill those connections and then restore that database from backup.

Oddly enough, the following commands do not assist whatsoever:
alter database MyDatabaseName set offline with rollback immediate
alter database MyDatabaseName set online
alter database MyDatabaseName set single_user with rollback immediate