does using a long delineator multiple times degenerate encryption security?

I need to condense multiple distinct pieces of data into a single encrypted string that can be decrypted and separated out later.

Before encrypting, I need to separate the data with some kind of delineator that will never be confused with the data.

I have chosen to use a single, constant 20 character hexadecimal delineator. For example:

data_piece
data_item
data_obj

becomes

data_piece214c1a16bb5236e7090cdata_item214c1a16bb5236e7090cdata_obj

which then becomes

vjXC4Xd7LU6aZX4QClZkU330XT39hnoLoQYIFNov39tPX96OKsid7mOBHwoVb4KspyvMpVPrsfHCUd1zbzXyETtgW5yF4b0oaK8Q%2FZCZN2XBvbfL3vooD%2FDLOza3%2FSrSNNzIW8oALZhv08LBzeg3DvgUgC8fg0xv4%2BCAEIQLIhM%3D

after running it through a standard RIJNDAEL encryption algorithm with a 256 bit key and a url encoder.

Does this repetition of a single delineator degenerate the security of the encryption if there are occasions when it may be used two dozen times? If so, should I use an array of unique delineators so that they are never repeated within the same string, or does the difference really not matter for practical encryption purposes?