Peptide-functionalized surfaces, composed of optimized L-peptides, show a high resistance toward nonspecific adsorption of proteins. As L-peptides are known to be prone to proteolytic degradation, the aim of this work is to enhance the stability against enzymatic degradation by using the all D-peptide mirror image of the optimized L-peptides and to determine if the all D-enantiomer retains the protein-resistant and antifouling properties. Two L-peptides and their D-peptide mirror images, some of them containing the nonproteinogenic amino acid alpha-aminoisobutyric acid (Aib), were synthesized and tested against non-specific adsorption of the proteins lysozyme and fibrinogen and the settlement of marine diatom Navicula perminuta and marine bacteria Cobetia marina. Both the D-enantiomer and the insertion of Aib protected the peptides from proteolytic degradation. Protein resistance was enhanced with the D-enantiomers while maintaining the resistance toward diatoms.